From eggs of var.Telamonideslaid on the last of May larvæ were obtained, which gave on June 22nd-26th, 122 pupæ. These, as fast as formed, were placed on ice in the refrigerator in small tin boxes, and when all the larvæ had become transformed the pupæ were transferred to a cylindrical tin box (4 in. diam. and 6 in. high), and packed in layers between fine shavings. The tin box was set in a small wooden one, which was put directly on the ice and kept there till July 20th. From that date, by an unfortunate accident, the box, instead of being kept on the surface of the ice in an ice-house, as was intended, was placed on straw near the ice, so that the action of the cold was modified, the outside pupæ certainly experiencing its full effects, but the inside ones were probably at a somewhat higher temperature. The ice failed on August 20th, so that the pupæ had been subjected to an equable low temperature in the refrigerator for three to four weeks, and to a lesser degree of cold in the ice-house for five weeks, the temperatureof the last place rising daily, as the ice had all thawed by August 20th. On opening the box it was found (probably owing to the cold not having been sufficiently severe) that the butterflies had commenced to emerge. Twenty-seven dead and crippled specimens were removed, together with several dead pupæ. One butterfly that had just emerged was taken out and placed in a box, and when its wings had fully expanded it was found to be a “Telamonidesof the most pronounced type.” The experimenter then states:—“Early in the morning I made search for the dead and rejected butterflies, and recovered a few. It was not possible to examine them very closely from the wet and decayed condition they were in, but I was able to discover the broad crimson band which lies above the inner angle of the hind wings, and which is usually lined on its anterior side with white, and is characteristic of eitherWalshiiorTelamonides, but is not found inMarcellus. And the tip only of the tail being white inWalshii, while both tip and sides are white inTelamonides, enabled me to identify the form as between these two. There certainly were noWalshii, but there seemed to be a singleMarcellus, and excepting that all wereTelamonides.”
The remaining pupæ were kept in a light room where 3Telamonidesemerged the following day, and by September 4th 14 specimens of the same variety had emerged, but noMarcellusor intermediate forms. From the 4th to the 20th of September a few moreTelamonidesappeared, but between the 4th and 15th of the month 12 out of 26 butterflies that had emerged were intermediate betweenTelamonidesandMarcellus, some approximating to one form and some to the other form. The first pureMarcellusappeared on September 4th, and was followed by one specimen on the 6th, 8th, 13th and 15th respectively. From this last date toOctober 3rd, 6 out of 10 wereMarcellusand 3 intermediate. On September 3rd, a specimen intermediate betweenTelamonidesandWalshiiemerged, “in which the tails were white tipped as inWalshii, but in size and other characters it wasTelamonides, though the crimson band might have belonged to either form.” Butterflies continued to emerge daily up to September 20th, after which date single specimens appeared at intervals of from four to six days, the last emergence being on October 16th. Thus, from the time the box was removed from the ice-house, the total period of emerging was fifty-seven days, some specimens having emerged before the removal of the box. With specimens ofP. Ajaxwhich appear on the wing the first season the natural pupal period is about fourteen days, individuals rarely emerging after a period of four to six weeks.
Between August 20th and October 16th, the 50 following butterfliesemerged:—
All these butterflies were very uniform in size, being about that of the ordinaryTelamonides. The specimens ofTelamonidesespecially were “strongly marked, the crimson band in a large proportion of them being as conspicuous as is usual inWalshii, and the blue lunules near the tail were remarkably large and bright coloured. Of theMarcellus, in addition to the somewhat reduced size, the tails were almost invariably shorter than usual and narrower, and instead of the characteristic single crimson spot, nearly all had two spots, often large. In all these particulars they approachTelamonides.”
Adding to theTelamonideswhich emerged after August 20th most of those specimens which were found dead in the box at that date, the total number of this form is thus brought up to nearly 50. Of the 122 pupæ with which Mr. Edwards started, 28 remained in a state fit for hibernation, several having died without emerging. Previous experiments had shown that 28 out of 122 pupæ is not an unreasonable number to hibernate, so that the author concludes that the butterflies which emerged the same season would have done so naturally, and the effect of the artificial cold was not “to precipitate the emerging of any which would have slept” till thefollowing spring. Now under ordinary circumstances all the butterflies which emerged the same season would have been of theMarcellusform, so that the cold changed a large part of these into the formTelamonides, some (probably from those pupæ which experienced the lowest temperature) being completely changed, and others (from those pupæ which were only imperfectly subjected to the cold) being intermediate,i.e., only partly changed. It appears also that several pupæ experienced sufficient cold to retard their emergence and stunt their growth, but not enough to change their form, these being the 13 recorded specimens ofMarcellus. Had the degree of cold been equal and constant, the reversion would probably have been more complete. The application of cold produced great confusion in the duration of the pupal period, the emergence, instead of taking place fourteen days after the withdrawal of the cold, as might have been expected from Dr. Weismann’s corresponding experiment withPieris Napi(Appendix I. Exps.13and 14), having been extended over more than two months.
From the results of this experiment it must be concluded thatTelamonidesis the primary form of the species.
[Communicated byMr.W. H. Edwards,November 18th, 1879.]
Exp.1.—In 1877 chrysalides ofP. AjaxandGrapta Interrogationis(the eggs laid by females of the formFabricii) were experimented upon; but the results were not satisfactory, for the reason that the author having been absent from home most of the time while the pupæ were in the ice-box, on his return found the temperature above 5°-6° R. And so far as could be told, the ice had been put in irregularly, and there might have been intervals during which no ice at all was in the box. Six chrysalidesof theGraptaso exposed produced unchangedUmbrosa, the co-form withFabricii. But all chrysalides from the same lot of eggs, and not exposed to cold, also producedUmbrosa. Nothing was learnt, therefore, respecting this species.
But chrysalides ofAjax, exposed at same time, did give changed butterflies to some extent. From a lot of 8, placed in the box when under twelve hours from pupation, and left for twenty-four days, there came 5 males and 3 females. Of these was 1Telamonidesin markings and coloration, and all the rest were betweenMarcellusandTelamonides. Two other chrysalides on ice for twenty-three days gaveTelamonides, but 3 more exposed twenty-six days, and all one hour old when put on ice, were unchanged, producingMarcellus.
During the same season 6 otherAjaxchrysalides were placed in the box, and kept at about 0°-1° R. One was one hour old, and remained for five days; 1 was one hour old, and remained for two days and three-quarters; 3 at three hours old for eight days; and 1 (age omitted), six days. All these gave unchanged butterflies of the formMarcellus.
Exp.2.—In May, 1878, many chrysalides were placed in the ice-box, being from eggs laid byAjax, var.Walshii. The youngest were but ten to fifteen minutes from pupation, and were soft; others at intervals up to twenty-four hours (the chrysalis is hard at about twelve hours); after that, each day up to eight days after pupation. All were removed from the box on the same day, 28th May. The exposure was from nineteen to five days, those chrysalides which were put on ice latest having the shortest exposure. The author wished to determine if possible whether, in order to effect any change, it was necessary that cold should be applied immediately after pupation or if one or several days might intervene between pupation and refrigeration. Inasmuch as no colour beginsto show itself in the pupæ till a few hours, or at most a day or two, before the butterfly emerges, it was thought possible that cold applied shortly before that time would be quite as effective as if applied earlier and especially very soon after pupation. The result was, that more than half of the chrysalides exposed before they had hardened died: 1 exposed at ten minutes, 2 at one hour, 1 at two hours, 2 at three hours after pupation. On the other hand 1 at fifteen minutes produced a butterfly, 1 at two hours, another at twelve hours. The temperature was from 0°-1° R. most of the time, but varied somewhat each day as the ice melted. The normal chrysalis period is from eleven to fourteen days, in case the butterfly emerges the same season, but very rarely an individual will emerge several weeks after pupation.
On the 14th day after taking the pupæ from the ice, 1Telamonidesemerged from a chrysalis which had been placed in the ice-box three days after pupation, and was on ice sixteen days.On 19th day, 1Telamonidesemerged from a pupa put on the ice twelve hours after pupation, and kept there eleven days.On 19th day, 1Walshiiemerged from a pupa two hours old, and on ice eleven days.
On the 14th day after taking the pupæ from the ice, 1Telamonidesemerged from a chrysalis which had been placed in the ice-box three days after pupation, and was on ice sixteen days.
On 19th day, 1Telamonidesemerged from a pupa put on the ice twelve hours after pupation, and kept there eleven days.
On 19th day, 1Walshiiemerged from a pupa two hours old, and on ice eleven days.
All the rest emergedMarcellus, unchanged, but at periods prolonged in a surprising way.
Five chrysalides lived through the winter, and all gaveTelamonidesin the spring of 1879.
It appeared, therefore, that the only effect produced by cold in all chrysalides exposed more than three days after pupation was to retard the emergence of the butterfly. But even in some of these earliest exposed, and kept on the ice for full nineteen days, the only effect seemed to be to retard the butterfly.
Exp.3.—In June, 1879, eggs of the formMarcelluswere obtained, and in due time gave 104 chrysalides. Of these one-third were placed in the ice-box at from twelve to twenty-four hours after pupation, and were divided into 3 lots.
Temperature 0°-1° R. most of the time, but varying somewhat as the ice melted. (Both in 1878 and 1879 Mr. Edwards watched the box himself, and endeavoured to keep a low temperature.)
Of the 69 chrysalides not exposed to cold, 34 gave butterflies at from eleven to fourteen days after pupation, and 1 additional male emerged 11th August, or twenty-two days at least past the regular period of the species.
Of the iced chrysalides, from lot No. 1 emerged 4 females at eight days and a half to nine days and a half after removal from the ice, and 5 are now alive (Nov. 18) and will go over the winter.
From lot No. 2 emerged 1 male and 5 females at eight to nine days; another male came out at forty days; and 5 will hibernate.
From lot No. 3 emerged 4 females at nine to twelve days; another male came out at fifty-four days; and 6 were found to be dead.
In this experiment the author wished to see as exactly as possible—First, in what points changes would occur.Second, if there would be any change in the shape of the wings, as well as in markings or coloration—that is, whether the shape might remain as that ofMarcellus, while the markings might be ofTelamonidesorWalshii; a summer form with winter markings. Third, to ascertain more closely than had yet been done what length of exposure was required to bring about a decided change, and what would be the effect of prolonging this period. After the experiments withPhyciodes Tharos, which had resulted in a suffusion of colour, the author hoped that some similar cases might be seen inAjax. The decided changes in 1878 had been produced by eleven and sixteen days’ cold. In 1877, an exposure of two days and three-quarters to eight days had failed to produce an effect.
From these chrysalides 11 perfect butterflies were obtained, 1 male and 10 females. Some emerged crippled, and these were rejected, as it was not possible to make out the markings satisfactorily.
From lot No. 1, fourteen days,came:—
1 female betweenMarcellusandTelamonides.2 females,Marcellus.
These 2Marcelluswere pale coloured, the light parts a dirty white; the submarginal lunules on hind wings were only two in number and small; at the anal angle was one large and one small red spot; the frontal hairs were very short. The first, or intermediate female, was also pale black, but the light parts were more green and less sordid; there were 3 large lunules; the anal red spot was double and connected, as inTelamonides; the frontal hairs short, as inMarcellus. These are the most salient points for comparing the several forms ofAjax. In nature, there is much difference in shape betweenMarcellusandTelamonides, still more betweenMarcellusandWalshii; and the latter may be distinguished from the other winter forms by the white tips ofthe tails. It is also smaller, and the anal spot is larger, with a broad white edging.
From lot No. 2, twenty days,came:—
1 femaleMarcellus, with single red spot.1 female betweenMarcellusandTelamonides; general coloration pale; the lunules all obsolescent; 2 large red anal spots not connected; frontal hairs medium length, as inTelamonides.1 female betweenMarcellusandTelamonides; colour bright and clear; 3 lunules; 2 large red spots; frontal hairs short.1 femaleTelamonides; colours black and green; 4 lunules; a large double and connected red spot; frontal hairs medium.2 femaleTelamonides; colours like last; 3 and 4 lunules; 2 large red spots; frontal hairs medium.
1 femaleMarcellus, with single red spot.
1 female betweenMarcellusandTelamonides; general coloration pale; the lunules all obsolescent; 2 large red anal spots not connected; frontal hairs medium length, as inTelamonides.
1 female betweenMarcellusandTelamonides; colour bright and clear; 3 lunules; 2 large red spots; frontal hairs short.
1 femaleTelamonides; colours black and green; 4 lunules; a large double and connected red spot; frontal hairs medium.
2 femaleTelamonides; colours like last; 3 and 4 lunules; 2 large red spots; frontal hairs medium.
From lot No. 3, twenty-five days,came:—
1 maleTelamonides; clear colours; 4 large lunules; 1 large, 1 small red spot; frontal hairs long.1 femaleTelamonides; medium colours; 4 lunules; large double connected red spot; frontal hairs long.
1 maleTelamonides; clear colours; 4 large lunules; 1 large, 1 small red spot; frontal hairs long.
1 femaleTelamonides; medium colours; 4 lunules; large double connected red spot; frontal hairs long.
In general shape all wereMarcellus, the wings produced, the tails long.
From this it appeared that those exposed twenty-five days were fully changed; of those exposed twenty days, 3 were fully, 2 partly, 1 not at all; and of those exposed fourteen days, 1 partly, 2 not at all.
The butterflies from this lot of 104 chrysalides, but which had not been iced, were put in papers. Taking 6 males and 6 females from the papers just as they came to hand, Mr. Edwards set them, and compared them with the iced examples.
Of the 6 males, 4 had 1 red anal spot only, 2 had 1 large 1 small; 4 had 2 green lunules on the hind wings, 2 had3, and in these last there was a 4th obsolescent, at outer angle; all had short frontal hairs.
Of the 6 females, 5 had but 1 red spot, 1 had 1 large 1 small spot; 5 had 2 lunules only, 1 had 3; all had short frontal hairs.
Comparing 6 of the females from the iced chrysalides, being those in which a change had more or less occurred, with the 6 females not iced:
1. All the former had the colours more intense, the black deeper, the light, green.2. In 5 of the former the green lunules on hind wings were decidedly larger; 3 of the 6 had 4 distinct lunules, 1 had 3, 1 had 3, and a 4th obsolescent. Of the 6 females not iced none had 4, 2 had 2, and a 3rd, the lowest of the row, obsolescent; 3 had 3, the lowest being very small; one had 3, and a 4th, at outer angle, obsolescent.3. In all the former the subapical spot on fore wing and the stripe on same wing which crosses the cell inside the common black band, were distinct and green; in all the latter these marks were either obscure or obsolescent.4. In 4 of the former there was a large double connected red spot, and in one of the 4 it was edged with white on its upper side; 2 had 1 large and 1 small red spot. Of the latter 5 had 1 spot only, and the 6th had 1 spot and a red dot.5. The former had all the black portions of the wing of deeper colour but less diffused, the bands being narrower; on the other hand, the green bands were wider as well as deeper coloured. Measuring the width of the outermost common green band along the middle of the upper medium interspace on fore wing in tenths of a millimetre, it was found to be as follows:
1. All the former had the colours more intense, the black deeper, the light, green.
2. In 5 of the former the green lunules on hind wings were decidedly larger; 3 of the 6 had 4 distinct lunules, 1 had 3, 1 had 3, and a 4th obsolescent. Of the 6 females not iced none had 4, 2 had 2, and a 3rd, the lowest of the row, obsolescent; 3 had 3, the lowest being very small; one had 3, and a 4th, at outer angle, obsolescent.
3. In all the former the subapical spot on fore wing and the stripe on same wing which crosses the cell inside the common black band, were distinct and green; in all the latter these marks were either obscure or obsolescent.
4. In 4 of the former there was a large double connected red spot, and in one of the 4 it was edged with white on its upper side; 2 had 1 large and 1 small red spot. Of the latter 5 had 1 spot only, and the 6th had 1 spot and a red dot.
5. The former had all the black portions of the wing of deeper colour but less diffused, the bands being narrower; on the other hand, the green bands were wider as well as deeper coloured. Measuring the width of the outermost common green band along the middle of the upper medium interspace on fore wing in tenths of a millimetre, it was found to be as follows:
Measuring the common black discal band across the middle of the lower medium interspace on fore wing:
In other words the natural examples were more melanic than the others.
No difference was found in the length of the tails or in the length and breadth of wings. In other words, the cold had not altered the shape of the wings.
Comparing 1 male iced with 6 males not iced:
1. The former had a large double connected red anal spot, edged with white scales at top. Of the 6 not iced, 3 had but 1 red spot, 2 had 1 large 1 small, 1 had 1 large and a red dot.2. The former had 4 green lunules; of the latter 3 had 3, 3 had only 2.3. The former had the subapical spot and stripe in the cells clear green; of the latter 1 had the same, 5 had these obscure or obsolescent.4. The colours of the iced male were bright; of the others, 2 were the same, 4 had the black pale, the light sordid white or greenish-white.
1. The former had a large double connected red anal spot, edged with white scales at top. Of the 6 not iced, 3 had but 1 red spot, 2 had 1 large 1 small, 1 had 1 large and a red dot.
2. The former had 4 green lunules; of the latter 3 had 3, 3 had only 2.
3. The former had the subapical spot and stripe in the cells clear green; of the latter 1 had the same, 5 had these obscure or obsolescent.
4. The colours of the iced male were bright; of the others, 2 were the same, 4 had the black pale, the light sordid white or greenish-white.
Looking over all, male and female, of both lots, the large size of the green submarginal lunules on the fore wings in the iced examples was found to be conspicuous as compared with all those not iced, though this feature is included in the general widening of the green bands spoken of.
In all the experiments withAjax, if any change at all has been produced by cold, it is seen in the enlarging or doubling of the red anal spot, and in the increased number of clear green lunules on the hind wings. Almost always the frontal hairs are lengthened and the colour of the wings deepened, and the extent of the black area isalso diminished. All these changes are in the direction ofTelamonides, or the winter form.
That the effect of cold is not simply to precipitate the appearance of the winter form, causing the butterfly to emerge from the chrysalis in the summer in which it began its larval existence instead of the succeeding year, is evident from the fact that the butterflies come forth with the shape ofMarcellus, although the markings may be ofTelamonidesorWalshii. And almost always some of the chrysalides, after having been iced, go over the winter, and then produceTelamonides, as do the hibernating pupæ in their natural state. The cold appears to have no effect on these individualchrysalides.59
With every experiment, however similar the conditions seem to be, and are intended to be, there is a difference in results; and further experiments—perhaps many—will be required before the cause of this is understood. For example, in 1878, the first butterfly emerged on the fourteenth day after removal from ice, the period being exactly what it is (at its longest) in the species in nature. Others emerged at 19–96 days. In 1879, the emergence began on the ninth day, and by the twelfth day all had come out, except three belated individuals, which came out at twenty, forty, and fifty-four days. In the last experiment, either the cold had not fully suspended the changes which the insect undergoes in the chrysalis, or its action was to hasten them after the chrysalides were taken from the ice. In the first experiment, apparently the changes were absolutely suspended as long as the cold remained.
It might be expected that the application of heat to the hibernating chrysalides would precipitate the appearance of the summer form, or change the markingsof the butterfly into the summer form, even if the shape of the wings was not altered; that is, to produce individuals having the winter shape but the summer markings. But this was not found to occur. Mr. Edwards has been in the habit for several years of placing the chrysalides in a warm room, or in the greenhouse, early in the winter, thus causing the butterflies to emerge in February, instead of in March and April, as otherwise they would do. The heat in the house is 19° R. by day, and not less than 3.5° R. by night. But the winter form of the butterfly invariably emerged, usuallyTelamonides, occasionallyWalshii.
Exp. 1.—In July, 1875, eggs ofP. Tharoswere obtained onAster Nova-Angliæin the Catskill Mountains, and the young larvæ, when hatched, taken to Coalburgh, West Virginia. On the journey the larvæ were fed on various species ofAster, which they ate readily. By the 4th of September they had ceased feeding (after having twice moulted), and slept. Two weeks later part of them were again active, and fed for a day or two, when they gathered in clusters and moulted for the third time, then becoming lethargic, each one where it moulted with the cast skin by its side. The larvæ were then placed in a cellar, where they remained till February 7th, when those that were alive were transferred to the leaves of anAsterwhich had been forced in a greenhouse, and some commenced to feed the same day. In due time they moulted twice more, making, in some cases, a total of five moults. On May 5th the first larva pupated, and its butterfly emerged after thirteen days. Another emerged on the 30th, after eight days pupal period, this stage being shortened as the weather became warmer. There emerged altogether 8 butterflies, 5 malesand 3 females, all of the formMarcia, and all of the variety designated C, except 1 female, which was var.B.60
Exp. 2.—On May 18th the first specimens (3 maleMarcia) were seen on the wing at Coalburgh; 1 female was taken on the 19th, 2 on the 23rd, and 2 on the 24th, these being all that were seen up to that date, but shortly after both sexes became common. On the 26th, 7 females were captured and tied up in separate bags on branches ofAster. The next day 6 out of the 7 had laid eggs in clusters containing from 50 to 225 eggs in each. Hundreds of caterpillars were obtained, each brood being kept separate, and the butterflies began to emerge on June 29th, the several stages being:—egg six days, larva twenty-two, chrysalis five. Some of the butterflies did not emerge till the 15th of July. Just after this date one brood was taken to the Catskills, where they pupated, and in this state were sent back to Coalburgh. There was no difference in the length of the different stages of this brood and the others which had been left at Coalburgh, and none of either lot became lethargic. The butterflies from these eggs of May were allTharos, with the exception of 1 femaleMarcia, var. C. Thus the first generation ofMarciafrom the hibernating larvæ furnishes a second generation ofTharos.
Exp. 3.—On July 16th, at Coalburgh, eggs were obtained from several females, allTharos, as no other form was flying. In four days the eggs hatched; the larval stage was twenty-two, and the pupal stage seven days; but, as before, many larvæ lingered. The first butterfly emerged on August 18th. All wereTharos, and noneof the larvæ had been lethargic. This was the third generation from the second laying of eggs.
Exp. 4.—On August 15th, at Coalburgh, eggs were obtained from a femaleTharos, and then taken directly to the Catskill Mountains, where they hatched on the 20th. This was the fourth generation from the third laying of eggs. In Virginia, and during the journey, the weather had been exceedingly warm, but on reaching the mountains it was cool, and at night decidedly cold. September was wet and cold, and the larvæ were protected in a warm room at night and much of the time by day, as they will not feed when the temperature is less than about 8° R. The first pupa was formed September 15th, twenty-six days from the hatching of the larvæ, and others at different dates up to September 26th, or thirty-seven days from the egg. Fifty-two larvæ out of 127 became lethargic after the second moult on September 16th, and on September 26th fully one half of these lethargic larvæ commenced to feed again, and moulted for the third time, after which they became again lethargic and remained in this state. The pupæ from this batch were divided into threeportions:—
A. This lot was brought back to Coalburgh on October 15th, the weather during the journey having been cold with several frosty nights, so that for a period of thirty days the pupæ had at no time been exposed to warmth. The butterflies began to emerge on the day of arrival, and before the end of a week all that were living had come forth, viz., 9 males and 10 females. “Of these 9 males 4 were changed toMarciavar. C, 3 were var. D, and 2 were not changed at all. Of the 10 females 8 were changed, 5 of them to var. B, 3 to var. C. The other 2 females were not different from manyTharosof the summer brood, having large discal patches on under side of hind wing, besides the markings common to the summer brood.”
B. This lot, consisting of 10 pupæ, was sent from the Catskills to Albany, New York, where they were kept in a cool place. Between October 21st and Nov. 2nd, 6 butterflies emerged, all females, and all of the var. B. Of the remaining pupæ 1 died, and 3 were alive on December 27th. According to Mr. Edwards this species never hibernates in the pupal state in nature. The butterflies of this lot were more completely changed than were those from the pupæ of lot A.
C. On September 20th 18 of the pupæ were placed in a tin box directly on the surface of the ice, the temperature of the house being 3°-4° R. Some were placed in the box within three hours after transformation and before they had hardened; others within six hours, and others within nine hours. They were all allowed to remain on the ice for seven days, that being the longest summer period of the chrysalis. On being removed they all appeared dead, being still soft, and when they had become hard they had a shrivelled surface. On being brought to Coalburgh they showed no signs of life till October 21st, when the weather became hot (24°-25° R.), and in two days 15 butterflies emerged, “every oneMarcia, not a doubtful form among them in either sex.” Of these butterflies 10 were males and 5 females; of the former 5 were var. C, 4 var. D, and 1 var. B, and of the latter 1 was var. C, and 4 var. D. The other 3 pupæ died. All the butterflies of this brood were diminutive, starved by the cold, but those from the ice were sensibly smaller than the others. All the examples of var. B were more intense in the colouring of the under surface than any ever seen by Mr. Edwards in nature, and the single male was as deeply coloured as the females, this also never occurring in nature.
Mr. Edwards next proceeds to compare the behaviourof the Coalburgh broods with those of the same species in theCatskills:—
Exp. 5.—On arriving at the Catskills, on June 18th, a few maleMarcia, var. D, were seen flying, but no females. This was exactly one month later than the first males had been seen at Coalburgh. The first female was taken on June 26th, another on June 27th, and a third on the 28th, allMarcia, var. C. Thus the first female was thirty-eight days later than the first at Coalburgh. No more females were seen, and noTharos. The three specimens captured were placed onAster, where two immediately depositedeggs61which were forwarded to Coalburgh, where they hatched on July 3rd. The first chrysalis was formed on the 20th, its butterfly emerging on the 29th, so that the periods were: egg six, larva seventeen, pupa nine days. Five per cent. of the larvæ became lethargic after the second moult. This was, therefore, the second generation of the butterfly from the first laying of eggs. All the butterflies which emerged wereTharos, the dark portions of the wings being intensely black as compared with the Coalburgh examples, and other differences of colour existed, but the general peculiarities of theTharosform were retained. This second generation was just one month behind the second at Coalburgh, and since, in 1875, eggs were obtained by Mr. Mead on July 27th and following days, the larvæ from which all hibernated, this would be the second laying of eggs, and the resulting butterflies the first generation of the following season.
Thus in the Catskills the species is digoneutic, the first generation beingMarcia(the winter form), and the second the summer form. A certain proportion of thelarvæ from the first generation hibernate, and apparently all those from the second.
Discussion of Results.—There are four generations of this butterfly at Coalburgh, the first beingMarciaand the second and thirdTharos. None of the larvæ from these were found to hibernate. The fourth generation under the exceptional conditions above recorded (Exp. 4) produced someTharosand moreMarciathe same season, a large proportion of the larvæ also hibernating. Had the larvæ of this brood been kept at Coalburgh, where the temperature remained high for several weeks after they had left the egg, the resulting butterflies would have been allTharos, and the larvæ from their eggs would have hibernated.
The altitude of the Catskills, where Mr. Edwards was, is from 1650 to 2000 feet above high water, and the altitude of Coalburgh is 600 feet. The transference of the larvæ from the Catskills to Virginia (about 48° lat.) andvice-versa, besides the difference of altitude, had no perceptible influence on the butterflies of the several broods except the last one, in which the climatic change exerted a direct influence on part of them both as to form and size. The stages of the June Catskill brood may have been accelerated to a small extent by transference to Virginia, but the butterflies reserved their peculiarities of colour. (See Exp.5.) So also was the habit of lethargyretained.62The May brood, on the other hand,taken from Virginia to the Catskills, suffered no retardation of development. (See Exp.2.) It might have been expected that all the larvæ of this last brood taken to the mountains would have become lethargic, but the majority resisted this change of habit. From all these facts it may be concluded “that it takes time to naturalize a stranger, and that habits and tendencies, even in a butterfly, are not to be changedsuddenly.”63
It has been shown thatTharosis digoneutic in the Catskills and polygoneutic in West Virginia, so that at a great altitude, or in a high latitude, we might expect to find the species monogoneutic and probably restricted to the winter formMarcia. These conditions are fulfilled in the Island of Anticosti, and on the opposite coast of Labrador (about lat. 50°), the summer temperature of these districts being about the same. Mr. Edwards states, on the authority of Mr. Cooper, who collected in the Island, thatTharosis a rare species there, but has a wide distribution. No specimens were seen later than July 29, after which date the weather became cold, and very few butterflies of any sort were to be seen. It seems probable that none of the butterflies of Anticosti or Labrador produce a second brood. All the specimens examined from these districts were of the winter form.
In explanation of the present case Dr. Weismann wrote to Mr. Edwards:—“Marciais the old primary form of the species, in the glacial period the only one.Tharosis the secondary form, having arisen in the course of many generations through the gradually working influence of summer heat. In your experiments cold has caused the summer generation to revert to the primary form. The reversion which occurred was complete in the females, but not in all the males. Thisproves, as it appears to me, that the males are changed or affected more strongly by the heat of summer than the females. The secondary form has a stronger constitution in the males than in the females. As I read your letter, it at once occurred to me whether in the spring there would not appear some males which were not pureMarcia, but were of the summer form, or nearly resembling it; and when I reached the conclusion of the letter I found that you especially mentioned that this was so! And I was reminded that the same thing is observable inA. Levana, though in a less striking degree. If we treated the summer brood ofLevanawith ice, many more females than males would revert to the winter form. This sex is more conservative than the male—slower to change.”
The extreme variability ofP. Tharoswas alluded to more than a century ago by Drury, who stated:—“In short, Nature forms such a variety of this species that it is difficult to set bounds, or to know all that belongs to it.” Of the different named varieties, according to Mr. Edwards, “A appears to be an offset of B, in the direction most remote from the summer form, just as inPapilio Ajax, the var.Walshiiis on the further side ofTelamonides, remote from the summer formMarcellus.” Var. C leads from B through D directly to the summer form, whilst A is more unlike this last variety than are several distinct species of the genus, and would not be suspected to possess any close relationship were it not for the intermediate forms. The var. B is regarded as nearest to the primitive type for the following reasons:—In the first place it is the commonest form, predominating over all the other varieties in W. Virginia, and moreover appears constantly in the butterflies from pupæ submitted to refrigeration. Its distinctive peculiarity of colour occurs in the allied speciesP. Phaon(Gulf States) andP. Vesta(Texas), both of which areseasonally dimorphic, and both apparently restricted in their winter broods to the form corresponding to B ofTharos. In their summer generation both these species closely resemble the summer form ofTharos, and it is remarkable that these two species, which are the only ones (with the exception of the doubtfulBatesii) closely allied toTharos, should alone be seasonally dimorphic out of the large number of species in the genus.
Mr. Edwards thus explains the case under consideration:—“WhenPhaon,Vesta, andTharoswere as yet only varieties of one species, the sole coloration was that now common to the three. As they gradually became permanent, or in other words, as these varieties became species,Tharoswas giving rise to several sub-varieties, some of them in time to become distinct and well marked, while the other two,PhaonandVesta, remained constant. As the climate moderated and the summer became longer, each species came to have a summer generation; and in these the resemblance of blood-relationship is still manifest. As the winter generations of each species had been much alike, so the summer generations which sprung from them were much alike. And if we consider the metropolis of the speciesTharos, or perhaps of its parent species, at the time when it had but one annual generation, to have been somewhere between 37° and 40° on the Atlantic slope, and within which limits all the varieties and sub-varieties of both winter and summer forms ofTharosare now found in amazing luxuriance, we can see how it is possible, as the glacial cold receded, that only part of the varieties of the winter form might spread to the northward, and but one of them at last reach the sub-boreal regions and hold possession to this day as the sole representative of the species. And at a very early period the primary form, together withPhaonandVesta, had made its way southward, where all three are found now.”
[Communicated byMr.W. H. EDWARDS,November 15th, 1879.]
The experiments with this species were made in June, 1879, on pupæ from eggs laid by the summer formUmbrosaof the second brood of the year, and obtained by confining a female in a bag on a stem of hop. As the pupæ formed, and at intervals of from six to twenty-four hours after pupation (by which time all the older ones had fully hardened), they were placed in the ice-box. In making this experiment Mr. Edwards had three objects in view. 1st. To see whether it was essential that the exposure should take place immediately after pupation, in order to effect any change. 2ndly. To see how short a period would suffice to bring about any change. 3rdly. Whether exposing the summer pupæ would bring about a change in the form of the resulting butterfly. Inasmuch as breeding from the egg ofUmbrosa, in June, in a formeryear,64gave bothUmbrosa(11) andFabricii(6), the butterflies from the eggs obtained, if left to nature, might be expected to be of both forms. The last or fourth brood of the year having been found up to the present time to beFabricii, and the 1st brood of the spring, raised from eggs ofFabricii(laid in confinement), having been found to be whollyUmbrosa, the latter is probably the summer andFabriciithe winter form. The two intervening broods,i.e.the 2nd and 3rd, have yielded both forms. This species hibernates in the imago state.
After the pupæ had been in the ice-box fourteen days they were all removed but 5, which were left in six days longer. Several were dead at the end of fourteen days. The temperature most of the time was 1°-2° R.; but fora few hours each day rose as the ice melted, and was found to be 3°-6° R.
From the fourteen-day lot 7 butterflies were obtained, 3 males and 4 females. From the twenty-day lot 4 males and 1 female; every oneUmbrosa. All had changed in one striking particular. In the normalUmbrosaof bothsexes,65the fore wings have on the upper side on the costal margin next inside the hind marginal border, and separated from it by a considerable fulvous space, a dark patch which ends a little below the discoidal nervule; inside the same border at the inner angle is another dark patch lying on the submedian interspace. Between these two patches, across all the median interspaces, the ground-colour is fulvous, very slightly clouded with dark.
In all the 4 females exposed to cold for fourteen days a broad black band appeared crossing the whole wing, continuous, of uniform shade, covering the two patches, and almost confluent from end to end with the marginal border, only a streak of obscure fulvous anywhere separating the two. In the case of the females from pupæ exposed for twenty days, the band was present, but while broad, and covering the space between the patches, it was not so dark as in the other females, and included against the border a series of obscure fulvous lunules. This is just like many normal females, and this butterfly was essentially unchanged.
In all the males the patches were diffuse, that at the apex almost coalescing with the border. In the 3 from chrysalides exposed fourteen days these patches were connected by a narrow dark band (very different from the broad band of the females), occupying the same position as the clouding of the normal male, but blackened and somewhat diffused. In the 4 examplesfrom the twenty-day pupæ, this connecting band was scarcely as deeply coloured and continuous as in the other 3. Beyond this change on the submarginal area, whereby a band is created where naturally would be only the two patches, and a slight clouding of the intervening fulvous surfaces, there was no difference of the upper surface apparent between these examples of both sexes, and a long series of natural ones placed beside them.
On the under side all the males were of one type, the colours being very intense. There was considerably more red, both dark and pale, over the whole surface, than in a series of natural examples in which shades of brown and a bluish hue predominate. No change was observed in the females on the under side.
It appears that fourteen days were as effective in producing changes as a longer period. In fact, the most decided changes were found in the females exposed the shorter period. It also appears that with this species cold will produce change if applied after the chrysalis has hardened. The same experiments were attempted in 1878 with pupæ ofGrapta Comma. They were put on ice at from ten minutes to six hours after forming, and subjected to a temperature of about 0°-1° R. for eighteen to twenty days, but every pupa was killed. Chrysalides ofPapilio Ajaxin the same box, and partly exposed very soon after pupation, were not injured. It was for this reason that none of theInterrogationispupæ were placed in the box till six hours had passed.
It appears further that cold may change the markings on one part of the wing only, and in cases where it does change dark or dusky markings melanises them; or it may deepen the colours of the under surface (as in the females of the present experiment). The females in the above experiment were apparently most susceptibleto the cold, the most decided changes having been effected in them.
The resulting butterflies were all of one form, although both might have been expected to appear under natural circumstances.
Dr. Weismann’s remarks on the foregoing experiments.—The author of the present work has, at my request, been good enough to furnish the following remarks upon Mr. Edward’s experiments withG. Interrogationis:—
The interesting experiments of Mr. Edwards are here principally introduced because they show how many weighty questions in connexion with seasonal dimorphism still remain to be solved. The present experiments do not offer adirectbut, at most, only anindirectproof of the truth of my theory, since they show that the explanation opposed to mine is also in this case inadmissible. Thus we have here, as withPapilio Ajax, two out of the four annual generations mixed,i.e., consisting of summer and winter forms, and the conclusion is inevitable that these forms were not produced by thegradualaction of heat or cold. When, from pupæ of the same generation which are developed under precisely the same external conditions, both forms of the butterfly are produced, the cause of their diversity cannot lie in these conditions. It must rather depend on causes innate in the organism itself,i.e., on inherited duplicating tendencies which meet in the same generation, and to a certain extent contend with each other for precedence. The two forms must have had their origin in earlier generations, and there is nothing against the view that they have arisen through the gradual augmentation of the influences of temperature.
In another sense, however, one might perceive, in the facts discovered by Edwards, an objection to my theory.
By the action of cold the formUmbrosa, which flies in June, was produced. Now we should be inclined toregard the var.Umbrosaas the summer form, and the var.Fabricii, which emerges in the autumn, hibernates in the imago state, and lays eggs in the spring, as the winter form. It would then be incomprehensible why the var.Umbrosa(i.e., the summer form) should be produced by cold.
But it is quite as possible that the var.Umbrosaas that the var.Fabriciiis the winter form. We must not forget that, in this species,not one of the four annual generations is exposed to the cold of winter in the pupal state. When, therefore, we have in such cases seasonal dimorphism, to which complete certainty can only be given by continued observations of this butterfly, which does not occur very commonly in Virginia, this must depend on the fact that the species formerly hibernated in the pupal stage. This question now arises, which of the existing generations was formerly the hibernating one—the first or the last?
Either may have done soà priori, according as the summer was formerly shorter or longer than now for this species. If the former were the case, the var.Fabriciiis the older winter form; were the latter the case, the var.Umbrosais the original winter form, as shall now be more closely established.
Should the experiments which Mr. Edwards has performed in the course of his interesting investigations be repeated in future with always the same results, I should be inclined to explain the case asfollows:—
It is not the var.Fabricii, butUmbrosa, which is the winter generation. By the northward migration of the species and the relative shortening of the summer, this winter generation would be pushed forward into the summer, and would thereby lose only a portion of the winter characters which it had till that time possessed. The last of the four generations which occurs in Virginia is extremely rare, so that it must be regarded either asone of the generations now supposed to be originating, or as one now supposed to be disappearing. The latter may be admitted. Somewhat further north this generation would be entirely suppressed, and the third brood would hibernate, either in the imago state or as pupæ or caterpillars. In Virginia this third generation consists of both forms. We may expect that further north, at least, where it hibernates as pupæ, it will consist entirely, or almost entirely, of the var.Umbrosa. Still further north in the Catskill Mountains, as Edwards states from his own observations, the species has only two generations, and one might expect that the var.Umbrosawould there occur as the winter generation.
Should the foregoing be correct, then the fact that the second generation assumes theUmbrosaform by the action of cold, as was the case in Edward’s experiments, becomes explicable. The new marking peculiar to this form produced by this means must be regarded as a complete reversion to the true winter form, the characters of which are becoming partly lost as this generation is no longer exposed to the influence of winter, but has become advanced to the beginning of summer.
The foregoing explanation is, of course, purely hypothetical; it cannot at present be asserted that it is the correct one. Many investigations based on a sufficiently large number of facts are still necessary to be able to attempt to explain this complicated case with any certainty. Neither should I have ventured to offer any opinion on the present case, did I not believe that even such a premature and entirely uncertain explanation may always be of use in serving the inventive principle,i.e., in pointing out the way in which the truth must be sought.
As far as I know, no attempt has yet been made to prove from a general point of view the interpolation of new generations, or the omission of single generationsfrom the annual cycle, with respect to causes and effects. An investigation of this kind would be of the greatest importance, not only for seasonal dimorphism, but also for the elucidation of questions of a much more general nature, and would be a most satisfactory problem for the scientific entomologist. I may here be permitted to develope in a purely theoretical manner the principles in accordance with which such an investigation should bemade:—
On the change in the number of generations of the annual cycle.—A change in the number of generations which a species produces annually must be sought chiefly in changes of climate, and therefore in a lengthening or shortening of the period of warmth, or in an increase or diminution of warmth within this period; or, finally, in both changes conjointly. The last case would be of the most frequent occurrence, since a lengthening of the period of warmth is, as a rule, correlated with an elevation of the mean temperature of this period, andvice versâ. Of other complications I can here perceive thefollowing:—
Climatic changes may beactiveorpassive,i.e., they occur by a change of climate or by a migration and extension of the species over new districts having another climate.
By a lengthening of the summer, as I shall designate the shorter portion of the whole annual period of warmth, the last generation of the year would be advanced further in its development than before; if, for instance, it formerly hibernated in the pupal state, it would now pass the winter in the imago stage. Should a further lengthening of the summer occur, the butterflies might emerge soon enough to lay eggs in the autumn, and by a still greater lengthening the eggs also might hatch, the larvæ grow up and hibernate as pupæ. In this manner we should have a new generation interpolated, owing tothe generation which formerly hibernated being made to recede step by step towards the autumn and the summer.By a lengthening of the summer there occurs therefore a retrogressive interruption of generations.
The exact opposite occurs if the summer should become shortened. In this case the last generation would no longer be so far developed as formerly; for instance, it might not reach the pupal stage, as formerly, at the beginning of winter, and would thus hibernate in a younger stage, either as egg or larvæ. Finally, by a continual shortening of the summer it would no longer appear at the end of this period but in the following spring; in other words, it would be eliminated.By a shortening of the summer accordingly the interruption of generations occurs by advancement.
The following considerations, which submit themselves with reference to seasonal dimorphism, are readily conceivable, at least, in so far as they can be arrived at by purely theoretical methods. Were the summer to become shorter the generation which formerly hibernated in the pupal stage would be advanced further into the spring. It would not thereby necessarily immediately lose the winter characters which it formerly possessed. Whether this would happen, and to what extent, would rather depend upon the intensity of the action of the summer climate on the generation in question, and on the number of generations which have been submitted to this action. Hitherto no attempts have been made to expose a monomorphic species to an elevated temperature throughout several generations, so as to obtain an approximate measure of the rapidity with which such climatic influences can bring about changes. For this reason we must for the present refrain from all hypothesis relating to this subject.
The disturbance of generations by the shortening of summer might also occur to a species in such a mannerthat the generation which formerly hibernated advances into the spring, the last of the summer generations at the same time reaching the beginning of winter. The latter would then hibernate in the pupal state, and would sooner or later also assume the winter form through the action of the cold of winter. We should, in this case, have two generations possessing more or less completely the winter form, the ancient winter generation now gradually losing the winter characters, and the new winter generation gradually acquiring these characters.
In the reverse case,i.e., by a lengthening of the summer, we should have the same possibilities only with the difference that the disturbance of generations would occur in a reverse direction. In this case it might happen that the former winter generation would become the autumnal brood, and more or less preserve its characters for a long period. Here also a new winter generation would be produced as soon as the former spring brood had so far retrograded that its pupæ hibernated.
I am only too conscious how entirely theoretical are these conjectures. It is very possible that observation of nature will render numerous corrections necessary. For instance, I have assumed that every species is able, when necessary, to adapt any one of its developmental stages to hibernation. Whether this is actually the case must be learnt from further researches; at present we only know that many species hibernate in the egg stage, others in the larval state, others as pupæ, and yet others in the perfect state. We know also that many species hibernate in several stages at the same time, but we do not know whether each stage of every species has an equal power of accommodation to cold. Should this not be the case the above conjectures would have to be considerably modified. To take up this subject, so as to completely master all the facts connected therewith,naturalists would have to devote their whole time and energy to the order Lepidoptera, which I have been unable to do.
From the considerations offered, it thus appears that the phenomena of seasonal dimorphism may depend on extremely complex processes, so that one need not be surprised if only a few cases now admit of certain analysis. We must also admit, however, that it is more advantageous to science to be able in the first place to analyze the simplest cases by means of breeding experiments, than to concern oneself in guessing at cases which are so complicated as to make it impossible at present to procure all the materials necessary for their solution.