FOOTNOTES:

Family.Species.I.BuprestidæTwo spruce-borers, species not determined.{1.Chlænius æstivus.II.Carabidæ{2.Chlænius pennsylvanicus.{3.Galerita bicolor.{1.Blepharida rhois.{2.Chelymorpha argus.{3.Coptocycla aurichalcea.III.Chrysomelidæ{4.Coptocycla guttata.{5.Doryphora decemlineata.{6.Odontota dorsalis.{7.Trirhabda virgata.{8.Trirhabda canadense.IV.CicindelidæCicindela primeriana.V.Coccinellidæ{Adalia bipunctata.{Epilachna borealis.VI.ScarabæidæEuphoria inda.VII.SilphidæSilpha americana.VIII.TenebrionidæTenebrio molitor.

(2) An odd chromosome, which behaves during the growth stage of the first spermatocytes like the "accessory" of the Orthoptera, has been found in 4 species of Coleoptera,[A]belonging to 3 families:

Family.Species.I. CarabidæAnomoglossus emarginatus.II. ElateridæTwo Elaters; species not determined.III. LampyridæEllychnia corrusca.

(3) In most of the species of Coleoptera examined, the unequal pair or the odd chromosome remains condensed during the growth period of the first spermatocyte, like the "accessory" of the Orthoptera and the various heterochromosomes of the Hemiptera.

(4) Several of these species of Coleoptera have a synizesis stage in which the spermatogonial number of short loops is massed at one side of the nucleus. This is followed by a synapsis stage in which the loops straighten and unite in pairs, forming longer loops which soonspread out in the nuclear space, and, with the exception of the heterochromosomes, unite to form a continuous spireme.

(5) In several of the species of Coleoptera and in Aphrophora, it has been shown that a body staining like chromatin develops in the spermatids, increasing in size for a time, then breaking up into granules and disappearing. This body evidently has no relation to the heterochromosomes, as it is the same for all of the spermatids. Its staining qualities suggest that it may be material derived from the chromosomes. It is finally dissolved in the karyolymph.

(6) In iron-hæmatoxylin preparations the heterochromosomes of the Coleoptera vary greatly in their staining properties during mitosis. In some species they stain exactly like the ordinary chromosomes, in others the larger one of the unequal pair holds the stain more tenaciously than the others and also than its smaller mate, and this is true in several cases where the heterochromosome is smaller than the other chromosomes, which destain more readily. The odd chromosome of the Elaters stains less deeply than the others in the first spermatocyte. In the growth stage they stain more deeply, as a rule, than the spireme, with iron-hæmatoxylin or thionin, stain red with safranin-gentian and green with Auerbach's methyl green-fuchsin combination.

(7)Aphrophora quadrangularisagrees with theAnasagroup of Hemiptera heteroptera in having a pair ofm-chromosomes and an odd chromosome in the spermatocytes, but differs from many of that group in that the odd chromosome divides in the second mitosis instead of the first. It also differs from other known forms in exhibiting heterochromosomes in certain stages of the oöcytes.

(8) The two species of Lepidoptera examined have an equal pair of heterochromosomes.

FOOTNOTES:[A]Aug.20, 1906.—Since this paper was prepared, 19 other species of Coleoptera have been studied. Of these, 17 have an unequal pair of heterochromosomes in the spermatocytes. Six belong to the Chrysomelidæ, making 14 of that family that have been examined. Representatives of 4 new families—Melandryidæ, Lamiinæ, Meloidæ, Cerambycinæ have been studied. In only two species—1 Elater and 1 Lampyrid—has the odd chromosome been found in place of the unequal pair. No species of Coleoptera has yet been examined in which one or the other of these two types of heterochromosomes does not occur in the spermatocytes. Of the 42 species of Coleoptera whose germ cells have been studied, 85.7 per cent are characterized by the presence of an unequal pair of heterochromosomes in the male germ cells, 14.3 per cent by the presence of an odd chromosome.

[A]Aug.20, 1906.—Since this paper was prepared, 19 other species of Coleoptera have been studied. Of these, 17 have an unequal pair of heterochromosomes in the spermatocytes. Six belong to the Chrysomelidæ, making 14 of that family that have been examined. Representatives of 4 new families—Melandryidæ, Lamiinæ, Meloidæ, Cerambycinæ have been studied. In only two species—1 Elater and 1 Lampyrid—has the odd chromosome been found in place of the unequal pair. No species of Coleoptera has yet been examined in which one or the other of these two types of heterochromosomes does not occur in the spermatocytes. Of the 42 species of Coleoptera whose germ cells have been studied, 85.7 per cent are characterized by the presence of an unequal pair of heterochromosomes in the male germ cells, 14.3 per cent by the presence of an odd chromosome.

In number of chromosomes there is great variation, the smallest number (16) having been found inOdontota dorsalis, and the largest (40) inSilpha americana. The difference in size is also very marked, as may be seen by comparing the spermatogonial plates in figures 3 and 58 with those shown in figures 94 and 141.

No other species of the Tenebrionidæ has yet been secured, and all of the other beetles examined differ in a marked degree fromTenebrio molitorin the growth stages of the spermatocytes. While inTenebriothe chromatin stains very dark throughout the growth stage, and the unequal pair can not be distinguished until the prophase of division ('05, plateVI, figs. 171-180), in most of the others there are very distinct synizesis and synapsis stages, following the last spermatogonial mitosis, then a spireme stage in which the condensed unequal pair of heterochromosomes or the odd chromosome is conspicuous in contrast with the pale spireme, whether the preparation is stained with iron-hæmatoxylin, gentian, or thionin. InTenebrio molitor, the unequal pair behaved in every respect like the other bivalent chromosomes. In the other forms, though it behaves during the two maturation divisions like the symmetrical bivalents, it remains condensed during the growth period like the "accessory" of the Orthoptera, the odd chromosome, "m-chromosomes," and "idiochromosomes" of the Hemiptera. In several cases the heterochromosomes of the Coleoptera are associated with a plasmosome (figs. 22, 23, 63, 132, 158, 217), as is often true in other orders. This peculiar pair of unequal heterochromosomes varies considerably in size during the growth stage in some of the species studied, but changes very little in form, differing in this respect from the "accessory" in some of the Orthoptera (McClung, '02) and from the large idiochromosome in some of the Hemiptera (Wilson, '05).

The odd chromosome, so far as it has been studied, behaves precisely like the larger member of the unequal pair without its smaller mate (figs. 219, 220, 226, 233). In the growth stage it remains condensed and either spherical or sometimes flattened against the nuclear membrane (figs. 217, 225, 231). In the first maturation mitosis it is attached to one pole of the spindle, does not divide, but goes to one of the two second spermatocytes (figs. 233, 235). In the second spermatocyte it divides with the other chromosomes, giving two equal classes of spermatids differing by the presence or absence of this odd chromosome.

All of the evidence at hand leads to the conclusion that in the Coleoptera, the univalent elements of all the pairs, equal and unequal, separate in the first spermatocyte mitosis and divide quantitatively in the second. In this respect the behavior of the chromosomes in this order appears to be much more uniform than in the Orthoptera and Hemiptera.

As has been seen above, the conditions in the Coleoptera, so far as the heterochromosomes are concerned, correspond very closely in final results with those in the Hemiptera heteroptera and the Orthoptera. In minor details these chromosomes are less peculiar in the Coleoptera than in either of the other orders. Even condensation during the growth stage is not universal, and synapsis of the heterochromosomes apparently occurs simultaneously with that of the ordinary chromosomes, instead of being delayed, as in many of the Hemiptera heteroptera.

Aphrophora(Hemiptera homoptera) agrees with theAnasagroup of the Hemiptera heteroptera in having a pair of condensedm-chromosomes, in the growth stage, but this pair is already united in synapsis when first seen. It differs fromAnasa, but agrees withBanasaandArchimerusin exhibiting a typical odd chromosome which goes to one pole without division in the first spermatocyte, and divides with the other chromosomes in the second spermatocyte. The odd chromosome in this species of Hemiptera, therefore, behaves like that in the Coleoptera and Orthoptera. The most interesting points in the results of this study of the germ cells ofAphrophorais the discovery of two pairs of condensed chromosomes in certain phases of the growth stages of the oöcytes. This has not been shown to be the case in any other species of Hemiptera, so far as I can ascertain. It is now evident that in the Heteroptera homoptera there are at least two distinct classes as to behavior of chromosomes. In one class we have the Aphids (Stevens, '05 and '06) and Phylloxera (Morgan, '06) in which no heterochromosomes have been found, while in the other class are such forms as Aphrophora with both a pair ofm-chromosomes and a typical odd heterochromosome.

The two species of Lepidoptera examined indicate that here we may have conditions comparable to those inNezara—an equal pair of heterochromosomes whose only apparent peculiarity is their condensed form during the growth stage. Doubtless the results of other investigators will soon throw more light on the heterochromosomes of this order.

It will be seen from the foregoing that the results obtained in the study of the germ cells ofTenebrio molitorhave been confirmed in full for several species of Coleoptera, and in part for 19[B]different species belonging to 8[B]families. It has also been shown that a different type of Coleopteran spermatogenesis exists in at least 3 families, where an odd chromosome like that in the Orthoptera occurs in place of the unequal pair. In all of these insects the spermatozoa are distinctly dimorphic, forming two equal classes, one of which either contains one smaller chromosome or lacks one chromosome.

The most difficult part of the work has been the determination of the somatic number of chromosomes in the male and female. In some cases suitable material has been lacking; in others, though material was abundant, no metaphases could be found in which the chromosomes were sufficiently separated to be counted with certainty. In three species (in addition toTenebrio molitor) where the unequal pair is present, the female somatic cells have been shown to contain the same number of chromosomes as the spermatogonia, but an equal pair in place of the unequal pair of the male. In two new cases the male somatic number and size have been shown to be the same as in the spermatogonia. In one of the Elateridæ, where the spermatogonial number is 19, the female somatic number is 20, and inAphrophorathe numbers in male and female cells are respectively 23 and 24. No exception has been found to the rule established by previous work on the Coleoptera (Stevens, '05) and on the Hemiptera (Wilson, '05 and '06), that (1) in cases where an unequal pair is present in the male germ cells, it is also present in the male somatic cells, but is replaced in the female by an equal pair, each component being equal in volume to the larger member of the unequal pair, and (2) in cases where an odd chromosome occurs in the male, a pair of equal size are found in the female. It is therefore evident that an egg fertilized by a spermatozoön (1) containing the small member of an unequal pair or (2) lacking one chromosome, must develop into a male, while an egg fertilized by a spermatozoön containing the larger element of an unequal pair of heterochromosomes or the odd chromosome must produce a female.

Whether these heterochromosomes are to be regarded as sex chromosomes in the sense that they both represent sex characters and determine sex, one can not decide without further evidence.

Comparison of the two types in Coleoptera, especially where, as in the Carabidæ, both occur in one family, has suggested to me that here it is possible that the small chromosome represents not a degenerate female sex chromosome, as suggested by Wilson, but some character or characters which are correlated with the sex character in some species and not in others. Assuming this to be the case, a pair of small chromosomes might be subtracted from the unequal pair, leaving an odd chromosome. The two types would then be reduced to one. It may be possible to determine the validity of this suggestion for particular cases by observation or experiment.

Since the first of this series of papers was published, there have appeared three important papers by Prof. E. B. Wilson, bearing on the problem of sex determination in insects. These papers are based on a study of many species of the Hemiptera heteroptera. These insects fall into two classes—one in which a pair of "idiochromosomes," usually of different size, remain separate and divide quantitatively in the first spermatocyte, conjugate and then separate in the second maturation mitosis; and another class in which an odd chromosome—the "heterotropic" chromosome—divides in one of the maturation mitoses, but not in the other. Wilson regards the odd chromosome as the equivalent of the larger of the "idiochromosomes," its smaller mate having disappeared. In the somatic cells of the former class he finds in the male the unequal pair, in the female an equal pair, the smaller chromosome being replaced by an equivalent of the larger "idiochromosome." In the latter class the male somatic cells contain the odd number, the female somatic cells and oögonia an even number, the homologue of the odd chromosome of the male being present and giving to the female one more chromosome than are found in the male.

In his latest paper Wilson ('06) makes a variety of suggestions as to sex determination. He shows that if the "idiochromosomes" and the heterotropic chromosome be regarded as sex chromosomes in the double sense that they both bear sex characters and determine sex, the following scheme accounts for the observed facts in all cases where an unequal pair or an odd heterochromosome have been found:

Sperm.Egg.{Large ♂ "idiochromosome"}I.{or}+Large ♀ sex chromosome=a ♀{Odd chromosome.}II.{Small ♀ "idiochromosome"}{or}+ Large ♂ sex chromosome=a ♂{No sex chromosome}

Here we know that such a combination of gametes must occur to give the observed results, but we are not certain that we have a right to attribute the sex characters to these particular chromosomes or in fact to any chromosomes. It seems, however, a reasonable assumption in accordance with the observed conditions. The scheme also assumes either selective fertilization or, what amounts to the same thing, infertility of gametic unions where like sex chromosomes are present. It also assumes that the large female sex chromosome is dominant in the presence of the male sex chromosome, and that the male sex chromosome is dominant in the presence of the small female sex chromosome. Or, it might rather be said that these are not really assumptions, but inferences as to what must be true if the heterochromosomes are sex chromosomes. This theory of sex determination brings the facts observed in regard to the heterochromosomes under Castle's modification of Mendel's Law of Heredity ('99).

The question of dominance is a difficult one, especially in parthenogenetic eggs and eggs which are distinctly male or female before fertilization. It may be possible that the sex character of the egg after maturation is always dominant in the fertilized egg, as appears to be the case in these insects (see scheme). Conditions external to the chromosomes may determine in certain cases, such as Dinophilus, which sex character shall dominate in the growing oöcyte, and maturation occur accordingly. It is evident that this reasoning would lead to the conclusion that sex is or may be determined in the egg before fertilization, and that selective fertilization, or infertility of gametic unions containing like sex characters, has to do, not with actual sex determination, but with suitable distribution of the sex characters to future generations. If both sex characters are present in parthenogenetic eggs, as appears to be the case in aphids and phylloxera, dominance of one or the other must be determined by conditions external to the chromosomes, for we have both sexes at different points in the same line of descent without either reduction or fertilization.

Wilson suggests as alternatives to the chromosome sex determinant theory according to Mendel's Law, (1) that the heterochromosomes may merely transmit sex characters, sex being determined by protoplasmic conditions external to the chromosomes; (2) That the heterochromosomes may be sex-determining factors only by virtue of difference in activity or amount of chromatin, the female sex chromosome in the male being less active. The first of these alternatives is an attempt to cover such cases asDinophilus,Hydatina, andPhylloxerawith large female and small male eggs. Here Morgan's ('06) suggestion as to degenerate males seems much to the point. The male sexcharacter, having become dominant in certain eggs at an early stage, may, from that time on, determine the kind of development. As to the second alternative, I see no reason for supposing that the small heterochromosome of a pair is in any different condition, as to activity, from the large one. The condensed condition may not mean inactivity, but some special form of activity. And, moreover, it has been shown that in certain stages of the development of the oöcyte of one form,Aphrophora quadrangularis, there are pairs of condensed chromosomes corresponding to those of the spermatocyte, so that there would hardly seem to be any basis for Wilson's attempt to associate the difference in development of male and female germ cells with activity or inactivity of chromosomes, as indicated by condensed or diffuse condition of the chromatin.

On the whole, the first theory, which brings the sex determination question under Mendel's Law in a modified form, seems most in accordance with the facts, and makes one hopeful that in the near future it may be possible to formulate a general theory of sex determination.

This work has been done in connection with a study of the problem of sex determination, but, whatever may be the final decision on that question, it brings together a mass of evidence in favor of the belief in both morphological and physiological individuality of the chromosomes, as advocated by Boveri, Sutton, and Montgomery. It also gives the strongest kind of evidence that maternal and paternal homologues unite in synapsis and separate in maturation, leaving the ripe germ cells pure with regard to each pair of characters.

Bryn Mawr College,June 7, 1906.

FOOTNOTES:[B]Aug.20, 1906.—36 species belonging to 12 families. See note, p. 49.

[B]Aug.20, 1906.—36 species belonging to 12 families. See note, p. 49.

Boveri, Th.

'02. Ueber mehrpolige Mitosen als Mittel zur Analyse des Zellkerns. Verh. d. phys.-med. Ges. Würzburg, N. F., vol. 35.

Castle, W. E.

'03. The heredity of sex. Bull. Mus. Comp. Zoöl. Harvard College, vol. 40, no. 4.

McClung, C. E.

'99. A peculiar nuclear element in the male reproductive cells of insects. Zoöl. Bull., vol. 2.'00. The spermatocyte divisions of the Acridiidæ. Kans. Univ. Quart., vol. 9, no. 1.'01. Notes on the accessory chromosome. Anat. Anz., vol. 20, nos. 8 and 9.'02. The accessory chromosome—sex-determinant? Biol. Bull., vol. 3, nos. 1 and 2.'02a. The spermatocyte divisions of the Locustidæ. Kans. Univ. Quart., vol. 1, no. 8.'05. The chromosome complex of orthopteran spermatocytes. Biol. Bull., vol. 9, no. 5.

'99. A peculiar nuclear element in the male reproductive cells of insects. Zoöl. Bull., vol. 2.

'00. The spermatocyte divisions of the Acridiidæ. Kans. Univ. Quart., vol. 9, no. 1.

'01. Notes on the accessory chromosome. Anat. Anz., vol. 20, nos. 8 and 9.

'02. The accessory chromosome—sex-determinant? Biol. Bull., vol. 3, nos. 1 and 2.

'02a. The spermatocyte divisions of the Locustidæ. Kans. Univ. Quart., vol. 1, no. 8.

'05. The chromosome complex of orthopteran spermatocytes. Biol. Bull., vol. 9, no. 5.

Montgomery, Thos. H., Jr.

'01. A study of the chromosomes of the germ-cells of Metazoa. Trans. Amer. Phil. Soc., vol. 20.'03. The heterotypic maturation mitosis in Amphibia and its general significance. Biol. Bull., vol. 4, no. 5.'01a. Further studies on the chromosomes of the Hemiptera heteroptera. Proc. Acad. Nat. Sci. Phila., 1901.'04. Some observations and considerations upon the maturation phenomena of the germ-cells. Biol. Bull., vol. 6, no. 3.'05. The spermatogenesis ofSyrbulaandLycosæand general considerations upon chromosome reduction and heterochromosomes. Proc. Acad. Nat. Sci. Phila., 1905.

'01. A study of the chromosomes of the germ-cells of Metazoa. Trans. Amer. Phil. Soc., vol. 20.

'03. The heterotypic maturation mitosis in Amphibia and its general significance. Biol. Bull., vol. 4, no. 5.

'01a. Further studies on the chromosomes of the Hemiptera heteroptera. Proc. Acad. Nat. Sci. Phila., 1901.

'04. Some observations and considerations upon the maturation phenomena of the germ-cells. Biol. Bull., vol. 6, no. 3.

'05. The spermatogenesis ofSyrbulaandLycosæand general considerations upon chromosome reduction and heterochromosomes. Proc. Acad. Nat. Sci. Phila., 1905.

Morgan, T. H.

'06. The male and female eggs of Phylloxerans of the Hickories. Biol. Bull., vol. 10, no. 5.

Nowlin, W. N.

'06. A study of the spermatogenesis ofCoptocycla aurichalceaandCoptocycla guttata. Journ. of Exp. Zoöl., vol. 3, no. 3.

Paulmier, F. C.

'99. The spermatogenesis ofAnasa tristis. Journ. of Morph., vol. 15.

de Sinéty.

'01. Recherches sur la biologie et l'anatomie des phasms. La Cellule, vol. 19.

Stevens, N. M.

'05. A study of the germ cells ofAphis rosæandAphis œnotheræ. Journ. of Exp. Zoöl., vol. 2, no. 3.'05a. Studies in spermatogenesis, with especial reference to the "accessory chromosome." Carnegie Inst. of Wash., pub. no. 36.'06. Studies on the germ cell of Aphids. Ibid., pub. no. 51.

'05. A study of the germ cells ofAphis rosæandAphis œnotheræ. Journ. of Exp. Zoöl., vol. 2, no. 3.

'05a. Studies in spermatogenesis, with especial reference to the "accessory chromosome." Carnegie Inst. of Wash., pub. no. 36.

'06. Studies on the germ cell of Aphids. Ibid., pub. no. 51.

Sutton, W. S.

'02. On the morphology of the chromosome group inBrachystola magna. Biol. Bull., vol. 4, no. 1.'03. The chromosomes in heredity. Biol. Bull., vol. 4, no. 5.

'02. On the morphology of the chromosome group inBrachystola magna. Biol. Bull., vol. 4, no. 1.

'03. The chromosomes in heredity. Biol. Bull., vol. 4, no. 5.

Wilson, E. B.

'05. Studies on chromosomes. I. The behavior of the idiochromosomes in Hemiptera. Journ. Exp. Zoöl., vol. 2, no. 3.'05a. The chromosomes in relation to the determination of sex in insects. Science, vol. 22, no. 564.'05b. Studies on chromosomes. II. The paired microchromosomes, idiochromosomes, and heterotropic chromosomes in Hemiptera. Journ. Exp. Zoöl., vol. 2, no. 4.'06. Studies on chromosomes. III. The sexual differences of the chromosome-groups in Hemiptera, with some considerations of the determination and inheritance of sex. Ibid., vol. 3, no. 1.

'05. Studies on chromosomes. I. The behavior of the idiochromosomes in Hemiptera. Journ. Exp. Zoöl., vol. 2, no. 3.

'05a. The chromosomes in relation to the determination of sex in insects. Science, vol. 22, no. 564.

'05b. Studies on chromosomes. II. The paired microchromosomes, idiochromosomes, and heterotropic chromosomes in Hemiptera. Journ. Exp. Zoöl., vol. 2, no. 4.

'06. Studies on chromosomes. III. The sexual differences of the chromosome-groups in Hemiptera, with some considerations of the determination and inheritance of sex. Ibid., vol. 3, no. 1.

[The figures were all drawn with Zeiss oil-immersion 2 mm., oc. 12, and have been reduced one-third, giving a magnification of 1,000 diameters.]

Fig.1. Equatorial plate from somatic tissues of a male pupa, 27 large chromosomes, 1 small one.

2. Equatorial plate from an egg follicle, 28 large chromosomes.

3. Equatorial plate of spermatogonium, 27 large chromosomes, 1 small one.

4. First spermatocyte, synizesis stage.

5. First spermatocyte, early spireme stage, showing unequal pair of chromosomes.

6-7. First spermatocyte, later growth stages.

8. First spermatocyte, prophase.

9-12. First spermatocyte, metaphase.

13. First spermatocyte, equatorial plate.

14-15. First spermatocyte, anaphase, showing separation of the elements of the unequal pair (lands).

16. First spermatocyte, daughter plates.

17. Second spermatocytes, equatorial plates.

18. Second spermatocytes, equatorial plates showing V-shaped chromosomes.

19. Second spermatocyte, early anaphase, the small chromosome in metakinesis.

20. Equatorial plate from egg follicle, 30 large chromosomes.

21. Equatorial plate of spermatogonium, 29 large chromosomes, 1 small one.

22. First spermatocyte, growth stage showing the heterochromosome group.

23. Heterochromosome group.p= plasmosome,l= large heterochromosome,s= small heterochromosome.

24-27. First spermatocyte, metaphase.

28. First spermatocyte, equatorial plate.

29. First spermatocyte, equatorial plate, small member of the unequal pair only present.

30. First spermatocyte, daughter plates.

31. Second spermatocytes, equatorial plates.

32-33. Second spermatocytes, prophase.

Figs.34-35. Equatorial plates from egg follicles, 11 equal pairs, no small chromosome.

36. Equatorial plate of spermatogonium, 21 large chromosomes, 1 small one.

37. First spermatocyte, synizesis stage.

38-40. First spermatocyte, synapsis stage.

41-43. First spermatocyte, bouquet stage after synapsis.

44-45. First spermatocyte, spireme stage showing the unequal pair of heterochromosomes.

46. First spermatocyte, prophase.

47-49. First spermatocyte, metaphase.

50-51. First spermatocyte, equatorial plates,xthe heterochromosome pair.

52. First spermatocyte, showing metakinesis of the unequal pair.

53. First spermatocyte, anaphase.

54-55. Second spermatocyte, equatorial plates.

56. Second spermatocyte, anaphase.

57. Equatorial plate of male somatic cell from walls of the testis, 15 large chromosomes, 1 small one.

58-59. Equatorial plates of spermatogonia, 15 large chromosomes, 1 small one.

60. Resting nucleus of spermatogonium, showing plasmosome (p).

61. First spermatocyte, synizesis stage.

62. First spermatocyte, synapsis stage.

63-64. First spermatocyte, spireme stage, showing the larger and smaller heterochromosome associated with a plasmosome.

65-68. First spermatocyte, prophases.

Figs.69-70. First spermatocyte, metaphase.

71. First spermatocyte, equatorial plate.

72. First spermatocyte, metaphase, showing metakinesis of the heterochromosomes.

73-74. First spermatocyte, anaphase.

75-76. Second spermatocyte, equatorial plates.

77. Second spermatocyte, showing metakinesis of the small chromosome (s).

78. Second spermatocyte, prophase, showing chromosomes longitudinally split.

79-80. Young spermatids,nthe chromatin nucleolus.

81-87. A series of stages in the development of the sperm head, showing the various phases in the history of the chromatin nucleolus (n).

88. Cross-sections of nearly mature sperm heads.

89-90. Equatorial plates of spermatogonia of abnormal individual, 15 large chromosomes, 2 small ones.

91. First spermatocyte from same testis, spireme stage, showing 2 small chromosomes associated with 1 large one and a plasmosome.

92. First spermatocyte from the same testis, metaphase showing a similar heterochromosome group.

93. Second spermatocyte from same testis, equatorial plate, showing 2 small chromosomes.

94. Equatorial plate of spermatogonium, 17 large chromosomes and 1 small one.

95. First spermatocyte, spireme stage, showing the unequal pair.

96-97. First spermatocyte, late prophases.

98. First spermatocyte, metaphase, showing chromosomes of different forms.

99-100. First spermatocyte, equatorial plate.

101. Unequal heterochromosome pair from a metaphase.

102. First spermatocyte, anaphase; ordinary chromosomes stippled to show more clearly the metakinesis of the unequal pair.

103. Second spermatocyte, equatorial plates.

104. Second spermatocyte, prophase.

105-106. Abnormal giant spermatids, probably in process of degeneration.

107. Equatorial plate of spermatogonium, 20 chromosomes. The 2 smallest are the unequal pair of heterochromosomes (lands).

108. Resting spermatogonium, showing plasmosome (p).

109. First spermatocyte, spireme stage.

Figs.110-111. First spermatocyte, prophases.

112-113. First spermatocyte, late prophase.

114-116. First spermatocyte, metaphase.

117. First spermatocyte, equatorial plate,xthe unequal pair.

118-120. First spermatocyte, anaphase.

121. First spermatocyte, daughter plates.

122. Second spermatocyte, prophase.

123. Second spermatocyte, equatorial plates.

124-125. Second spermatocyte, daughter plates of the two classes.

126-127. Second spermatocyte, anaphase.

128-130. Spermatids,nthe chromatin nucleolus.

131-132. First spermatocyte, spireme stages, showing the heterochromosome group.

133-135. First spermatocyte, beginning of metakinesis.

136. First spermatocyte, equatorial plate,xthe unequal pair.

137. First spermatocyte, late anaphase, showing the heterochromosomeslands.

138. Second spermatocyte, equatorial plates.

139-140. Second spermatocyte, daughter plates of the two classes.

141. Equatorial plate of spermatogonium, 40 chromosomes—39 large, 1 small.

142. Resting nucleus of spermatogonium, showing 2 plasmosomes (p).

143-144. First spermatocyte, spireme stage.

145. First spermatocyte, prophase.

146-147. First spermatocyte, metaphase.

148. First spermatocyte, equatorial plate.

149. Second spermatocyte, equatorial plates.

150. Second spermatocyte, showing metakinesis of the small chromosome.

Figs.151-152. Equatorial plates of spermatogonia, 36 chromosomes—35 large, 1 small.

153. First spermatocyte, synizesis stage.

154. First spermatocyte, synapsis stage.

155-158. First spermatocyte, spireme stages.

159. First spermatocyte, spireme segmented and split.

160-163. First spermatocyte, prophases.

164-171. First spermatocyte, metaphase.

172. First spermatocyte, anaphase.

173-174. First spermatocyte, equatorial plates.

175-176. First spermatocyte, late anaphase.

177. Second spermatocyte, equatorial plates.

178-179. Second spermatocyte, telophase,a1, archoplasmic material.

180-186. Spermatids in different stages;a1, archoplasmic material from first spermatocyte spindle,a2archoplasmic material from second maturation spindle.

187. First spermatocyte, metaphase.

188-189. First spermatocyte, equatorial plates of two species, 10 and 11 chromosomes.

190. First spermatocyte, anaphase.

191. Second spermatocyte, equatorial plates containing 9 large chromosomes and 1 small one.

192. Chromosomes from prophase of the first spermatocyte, all from the same cyst.

Fig.193. Equatorial plate of spermatogonium, 20 chromosomes—19 large, 1 small.

194. First spermatocyte, spireme stage,xthe heterochromosome group.

195. First spermatocyte, metaphase.

196. First spermatocyte, equatorial plate.

197. Second spermatocyte, equatorial plates.

198. Equatorial plate of spermatogonium, 20 chromosomes—19 large, 1 small.

199. First spermatocyte, spireme stage,xthe heterochromosome group.

200. First spermatocyte, prophase.

201. First spermatocyte, metaphase,xthe unequal pair in tripartite form.

202. First spermatocyte, showing metakinesis of the heterochromosomes (lands).

203. First spermatocyte, equatorial plate.

204. Second spermatocyte, equatorial plates.

205. Giant spermatocyte, spireme stage, heterochromosome group double the usual size.

206. Giant spermatocyte, prophase.

207. First spermatocyte, spireme stage, showing the unequal pair associated with a large plasmosome.

208. First spermatocyte, metaphase.

209-210. First spermatocyte, beginning of metakinesis.

211. First spermatocyte, equatorial plate, 17 chromosomes.

212. First spermatocyte, anaphase, showing elongated centrosome and diverging univalent chromosomes.

213. First spermatocyte, spireme stage.

214. First spermatocyte, equatorial plate,xthe unequal bivalent.

215. First spermatocyte, late prophase.

Galerita bicolor(Family Carabidæ).

216. Equatorial plate of spermatogonium, 30 chromosomes—29 large, 1 small.

217. First spermatocyte, growth stage,xthe odd chromosome.

218. First spermatocyte, prophase.

219-220. First spermatocytes, metaphase,xthe odd chromosome.

221. First spermatocyte, equatorial plate.

222. First spermatocyte, daughter plates containing 18 and 19 chromosomes, respectively.

223. Second spermatocytes, equatorial plates.

224. Equatorial plate of spermatogonium, 19 chromosomes,xthe odd one.

225. First spermatocyte, spireme stage,xthe odd chromosome.

226. First spermatocyte, metaphase.

227. First spermatocyte, prophase.

228. First spermatocyte, equatorial plate.

229. Equatorial plate from egg follicle, 20 chromosomes,x1andx2the pair corresponding toxin the spermatogonium.

230. Equatorial plate of spermatogonium, 19 chromosomes,xthe odd one.

231. First spermatocyte, spireme stage.

232. First spermatocyte, prophase.

233. First spermatocyte, beginning of metakinesis.

234. First spermatocyte, equatorial plate,xthe odd chromosome.

235. A pair of second spermatocytes in metaphase, two chromosomes connected,xthe odd chromosome.

236. Equatorial plate of spermatogonium, 19 chromosomes.

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