1. Bred from eggs laid by a female of the winter form on 12th-15th May, 1868, in a breeding-cage. The caterpillars emerged on 20th-22nd May, and pupated on 7th-9th June. The pupæ, kept at the ordinary temperature,produced:—
All these butterflies were of theProrsatype, 3 females having a considerable amount of yellow, but none with so much as figs. 3, 4, 7, 8, or 9.Pl. I.
2. August 12th, 1868, found larvæ of the third generation, which pupated at the beginning of September, and were kept in a room not warmed. In September three butterflies emerged in theProrsaform, the remainder hibernating and producing, after being placed in a heated room at the end of February, from the 1st to the 17th of March, 1869, more butterflies, all of theLevanaform.
3. Larvæ found on the 17th June, 1869, were sorted according to colour; the yellow ones, with light brown spines, produced, at the ordinary temperature, on 8th-12th July, 13 butterflies, 12 of which showed the ordinaryProrsatype, and one, a male, possessing more yellow than fig. 3,Pl. I., must be considered as aPorimatype.
4. From caterpillars of the second generation, found at the same time as those of Exp.3, 30 pupæ were placed in the refrigerator (temperature 8°-10° R.) on June 25th. When the box was opened on August 3rd, almost all had emerged, many being dead, and all, without exception, were of the intermediate form (Porima), although nearer theProrsathan theLevanatype.
5. A large number of caterpillars of the second generation, found at the same time, pupated, and were kept at a high summer temperature. After a pupal period of about 19 days, some 70 butterflies emerged from 28th June to 5th July, all of theProrsaform, with the exception of 5, which were strongly marked with yellow (Porima).
6. The 70 butterflies of the foregoing experiment were placed in an enclosure 6 feet high, and 8 feet long, in which, during warm weather, they freely swarmed on flowers. Copulation was only once observed, and but one female laid eggs on nettle on July 4th. At the high summer temperature prevailing at the time, these eggs produced butterflies after 30–31 days (third generation). All wereProrsa, with more or less yellow; among 18 none were completelyPorima.
7. Young larvæ of the fourth generation, found on the 8th of August, were reared in a hothouse (17°-20° R.). They pupated on 21st-23rd August. Ofthese:—
A. 56 pupæ were placed on ice (0°-1° R.) for five weeks, and then allowed to hibernate in a roomnot warmed. In April, 1870, they all gave theLevanaform, with the exception of a singlePorima.
B. About an equal number of pupæ were placed in the hothouse, but without any result; for, notwithstanding a temperature of 12°-24° R., not a single butterfly emerged in the course of October and November. The pupæ were then allowed to hibernate in an unheated room, and in April and May gave nothing butLevana.
8. Caterpillars of the second generation, found at the beginning of June, 1870, pupated on 13th-15th June, and gave, at the ordinary temperature, on June 29th-30th, 7 butterflies of theProrsaform.
9. Pupæ of the same (second) generation were placed immediately after pupation on June 18th, 1870, in a refrigerator (0°-1° R.), and after remaining there four weeks (till July 18th) gave, at the ordinary summertemperature:—
Of these 20 butterflies only 5 were of the pureProrsaform.
10. Full grown larvæ of the fourth generation, found on August 20th, 1870, pupated on August 26th to September 5th. The pupæ were divided into threeportions:—
A. Placed in the hothouse (12°-25° R.), immediately after pupation and left there till October 20th. Ofabout 40 pupæ only 4 emerged, 3 of which wereProrsaand 1Porima. The remaining pupæ hibernated and all changed intoLevanathe following spring.
B. Kept in a room heated to 6°-15° R. from November. Not a single specimen emerged the same year. This lot of pupæ were added to C from November.
C. Placed on ice for a month immediately after pupation; then, from September 28th to October 19th in the hothouse, where no more butterflies emerged. The pupæ hibernated, together with those from lot B, in a room heated by water to 6°-15° R., andgave:—
The exact record of the time of emergence is interesting, because it is thereby rendered apparent that different individuals respond more in different degrees to a higher than to the ordinary temperature. Whilst with many an acceleration of development of 1–2 months occurred, others emerged in April and May, i.e. at the time of their appearance in the natural state.
11. Reared the second generation from eggs of the first generation. Emerged from the eggs on June 6th, 1872, pupated on July 9th. The pupæ were placed on ice (0°-1° R.) from July 11th till September 11th, and then transferred to a hothouse, where allemerged:—
It must be pointed out, however, that among those specimens marked as “Levana” there were none which entirely corresponded with the naturalLevana, or which indeed approximated so nearly to this form as did some of the specimens in Exp.9. All were larger than the naturalLevana, and possessed, notwithstanding the large amount of yellow, more black than any trueLevana. In all artificially bredLevanathe black band of the basal half of the hind wings is always interrupted with yellow, which is seldom the case with trueLevana. The whole appearance of the artificialLevanais also coarser, and the contour of the wings somewhat different, the fore-wings being broader and less pointed. (See figs. 7 to 9,Pl. I.).
12. Larvæ of the fourth generation, found on September 22nd, 1872, were divided into twoportions:—
A. Placed for pupation in an orchid-house at 12°-25° R., and allowed to remain there till December. In spite of the high temperature not a single butterfly emerged during this time, whilst pupæ ofVanessa C-albumandPyrameis Atalanta, found at the same time, and placed in the same hothouse, emerged in the middle of October. From the middle of December the pupæ were kept in an unheated room, and they emerged very late in the spring of 1873, all asLevana:—
B. Kept in an unheated room during the winter. The butterflies emerged from the 28th of May, all asLevana.
13. Females ofPieris Rapæ, captured in April, laid eggs onSisymbrium Alliaria. From these caterpillars were obtained, which pupated on 1st-3rd June. The pupæ were placed on ice from June 3rd till September 11th (0°-1° R.), and from September 11th till October 3rd in the hothouse (12°-24° R.), where thereemerged:—
All these were sharply impressed with the characters of the winter form, the females all strongly yellow on the upper side, the males pure white; on the under side a strong black dusting on the hind wings, particularly on the discoidal cell. One pupa did not emerge in the hothouse, but hibernated, and gave in a heated room on January 20th, 1873, a female, also of the winter form.
14. Females ofPieris Napi, captured on 27th-28th April, 1872, laid eggs onSisymbrium Alliaria. The larvæ bred from these pupated on May 28th to June 7th. The pupæ, shortly after transformation, were placed on ice, where they remained till Sept. 11th (three months). Transferred to the hothouse on October 3rd, they produced, up to October 20th, 60 butterflies, all with the sharply-defined characters of the winter form. The remaining pupæ hibernated in a room, andproduced:—
15. Several butterflies from Exp.14, which emerged in May, 1873, were placed in a capacious breeding-house, where they copulated and laid eggs on rape. The caterpillars fed on the living plants in the breeding-house, and after pupation were divided into twoportions:—
A. Several pupæ, kept at the ordinary summer temperature, gave butterflies on July 2nd, having the characters of the summer form.
B. The remainder of the pupæ were placed on ice immediately after transformation, and remained over three months in the refrigerator (from July 1st till October 10th). Unfortunately most of them perished through the penetration of moisture into the box. Only 8 survived, 3 of which emerged on the 20th of October as the winter form; the others hibernated in an unheated room, and emerged at the beginning of June, 1874. All 5 were females, and all exhibited the characters of the winter form. Notwithstanding a pupal period of eleven months, they did not possess these characters to a greater extent than usual, and did not, therefore, approximate to the parent-formBryoniæ.
16. On June 12th, 1871, specimens ofPieris Napi, var.Bryoniæ, were captured on a mountain in the neighbourhood of Oberstorf (Allgäuer Alpen), and placed in a breeding-house, where they flew freely about the flowers; but although copulation did not take place, several females laid eggs on the ordinary garden cabbage. From these caterpillars were hatched, which at all stages of growth were exactly like those of the ordinary form ofNapi. They throve well until shortly before pupation, when a fungoid epidemic decimated them, so that from 300 caterpillars only about 40 living pupæ were obtained. These also completely resembled the ordinary form ofNapi, and showed the same polymorphism, some being beautifully green, others (the majority) straw yellow, and others yellowish grey. Only one butterfly emerged the same summer, a male, which, by the blackdusting of the veins on the margin of the wings (upper side), could be with certainty recognized as var.Bryoniæ. The remaining pupæ hibernated in a heated room, and gave, from the end of January to the beginning of June, 10 males and 5 females, all with the characters of the var.Bryoniæ. Theyemerged:—
We here perceive that the tendency to accelerate development through the action of warmth is, in this case, also very different in different individuals. Of the 16 butterflies only 1 kept to the normal period of development from July 27th to June 3rd, fully ten months; all the others had this period abbreviated, 1 male to eleven days, 8 specimens to six months, 4 to seven months, 2 to eight months, and 1 to nine months.