Section 278 the "bouquet" Was Cut Through, Showing the Bivalent

corresponding to the larger pair in figure 271, and in figure 279 this element is seen behind the paler loops. The history of these two pairs of heterochromosomes, which have not, so far as I know, been found before in oöcytes, should be followed up in older ovaries, and related species should be examined for similar phenomena.

LEPIDOPTERA.

Cacoecia and Euvanessa.

I had no intention of making an extended study of the spermatogenesis of the Lepidoptera, but was interested to see if anything corresponding to the heterochromosomes of other orders could be found. The material studied was the testes of the larvæ of Cacoecia cerasivorana and Euvanessa antiopa. The number of chromosomes is large, but the equatorial plates are diagrammatically clear. In both species 30 chromosomes are found in both first and second spermatocytes. In both, one chromosome is larger (figs. 290 and 293, x). In the growth stage (figs. 283, 284) there is a two-lobed body (or sometimes two separate spherical bodies) which seems to correspond in size to the larger pair of chromosomes in the first spermatocyte. In iron-hæmatoxylin preparations this pair is often obscured by parts of the spireme which are tangled around it. In safranin-gentian preparations it stains, not like a plasmosome, but red like the heterochromosomes, while the spireme is violet. The staining reaction at least suggests that this equal pair of chromosomes, which may be traced through the synizesis stage (fig. 280), synapsis stage (figs. 281, 282), growth stages (figs. 283, 284), and prophases (figs. 285-287), into the first spermatocyte spindle (figs. 288, 290), and on to the second spermatocyte (figs. 289, 291, 292), is an equal pair of heterochromosomes comparable to the equal pair of "idiochromosomes" found by Wilson in Nezara ('05). As the various stages are practically the same in Euvanessa antiopa, but somewhat clearer in Cacoecia, only one figure is given for Euvanessa--the equatorial plate of the first spermatocyte (fig. 293).

SUMMARY OF RESULTS.

(1) An unequal pair of heterochromosomes has been found by the author in 19 species of Coleoptera belonging to 8 families:

FAMILY. SPECIES.

I. Buprestidæ Two 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. Cicindelidæ Cicindela primeriana.

V. Coccinellidæ { Adalia bipunctata. { Epilachna borealis.

VI. Scarabæidæ Euphoria inda.

VII. Silphidæ Silpha americana.

VIII. Tenebrionidæ Tenebrio 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, belonging to 3 families:

FAMILY. SPECIES.

I. Carabidæ Anomoglossus emarginatus.

II. Elateridæ Two Elaters; species not determined.

III. Lampyridæ Ellychnia 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 soon spread 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 quadrangularis agrees with the Anasa group of Hemiptera heteroptera in having a pair of m-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:

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.

COMPARISON OF RESULTS IN DIFFERENT SPECIES OF COLEOPTERA.

In number of chromosomes there is great variation, the smallest number (16) having been found in Odontota dorsalis, and the largest (40) in Silpha 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 from Tenebrio molitor in the growth stages of the spermatocytes. While in Tenebrio the chromatin stains very dark throughout the growth stage, and the unequal pair can not be distinguished until the prophase of division ('05, plate VI, 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. In Tenebrio 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.

COMPARISON OF THE COLEOPTERA WITH THE HEMIPTERA AND LEPIDOPTERA.

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 the Anasa group of the Hemiptera heteroptera in having a pair of condensed m-chromosomes, in the growth stage, but this pair is already united in synapsis when first seen. It differs from Anasa, but agrees with Banasa and Archimerus in 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 of Aphrophora is 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 of m-chromosomes and a typical odd heterochromosome.

The two species of Lepidoptera examined indicate that here we may have conditions comparable to those in Nezara--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.

GENERAL DISCUSSION.

It will be seen from the foregoing that the results obtained in the study of the germ cells of Tenebrio molitor have been confirmed in full for several species of Coleoptera, and in part for 19 different species belonging to 8 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 to Tenebrio 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 in Aphrophora the 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 [Female] sex chromosome = a [Female] {Odd chromosome. }

II. {Small [Female] "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 as Dinophilus, Hydatina, and Phylloxera with large female and small male eggs. Here Morgan's ('06) suggestion as to degenerate males seems much to the point. The male sex character, 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:

AUG. 20, 1906.--36 species belonging to 12 families. See note, p. 49.

BIBLIOGRAPHY.

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.

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 of Syrbula and Lycosæ and 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 of Coptocycla aurichalcea and Coptocycla guttata. Journ. of Exp. Zoöl., vol. 3, no. 3.

PAULMIER, F. C.

'99. The spermatogenesis of Anasa 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 of Aphis rosæ and Aphis oenotheræ. 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 in Brachystola 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.

DESCRIPTION OF PLATES

PLATE VIII.

Trirhabda virgata (Family Chrysomelidæ).

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 (l and s).

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.

Trirhabda canadense.

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.

N. M. S. del.

COLEOPTERA]

PLATE IX.

Chelymortha argus (Family Chrysomelidæ).

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, x the 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.

Odontota dorsalis (Family Chrysomelidæ).

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.

N. M. S. del.

COLEOPTERA]

PLATE X.

Odontota dorsalis.

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, n the 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.

Epilachna borealis (Family Coccinellidæ).

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.

Euphoria inda (Family Scarabæidæ).

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

108. Resting spermatogonium, showing plasmosome (p).

109. First spermatocyte, spireme stage.

N. M. S. del.

COLEOPTERA]

PLATE XI.

Euphoria inda.

FIGS. 110-111. First spermatocyte, prophases.

112-113. First spermatocyte, late prophase.

114-116. First spermatocyte, metaphase.

117. First spermatocyte, equatorial plate, x the 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, n the chromatin nucleolus.

Blepharida rhois (Family Chrysomelidæ).

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

133-135. First spermatocyte, beginning of metakinesis.

136. First spermatocyte, equatorial plate, x the unequal pair.

137. First spermatocyte, late anaphase, showing the heterochromosomes l and s.

138. Second spermatocyte, equatorial plates.

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

Silpha americana (Family Silphidæ).

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.

N. M. S. del.

COLEOPTERA]

PLATE XII.

Doryphora decemlineata (Family Chrysomelidæ).

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, a{1}_, archoplasmic material.

180-186. Spermatids in different stages; a{1}, archoplasmic material from first spermatocyte spindle, a{2} archoplasmic material from second maturation spindle.

Spruce-borers (Family Buprestidæ).

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.

N. M. S. del

COLEOPTERA]

PLATE XIII.

Adalia bipunctata (Family Coccinellidæ).

FIG. 193. Equatorial plate of spermatogonium, 20 chromosomes--19 large, 1 small.

194. First spermatocyte, spireme stage, x the heterochromosome group.

195. First spermatocyte, metaphase.

196. First spermatocyte, equatorial plate.

197. Second spermatocyte, equatorial plates.

Cicindela primeriana (Family Cicindelidæ).

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

199. First spermatocyte, spireme stage, x the heterochromosome group.

200. First spermatocyte, prophase.

201. First spermatocyte, metaphase, x the unequal pair in tripartite form.

202. First spermatocyte, showing metakinesis of the heterochromosomes (l and s).

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.

Chlænius æstivus (Family Carabidæ).

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.

Chlænius pennsylvanicus.

213. First spermatocyte, spireme stage.

214. First spermatocyte, equatorial plate, x the unequal bivalent.

215. First spermatocyte, late prophase.

Galerita bicolor (Family Carabidæ).

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

Anomoglossus emarginatus (Family Carabidæ).

217. First spermatocyte, growth stage, x the odd chromosome.

218. First spermatocyte, prophase.

219-220. First spermatocytes, metaphase, x the odd chromosome.

221. First spermatocyte, equatorial plate.

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

223. Second spermatocytes, equatorial plates.

Elater I (Family Elateridæ, species not determined).

224. Equatorial plate of spermatogonium, 19 chromosomes, x the odd one.

225. First spermatocyte, spireme stage, x the odd chromosome.

226. First spermatocyte, metaphase.

227. First spermatocyte, prophase.

228. First spermatocyte, equatorial plate.

229. Equatorial plate from egg follicle, 20 chromosomes, x{1} and x{2} the pair corresponding to x in the spermatogonium.

Elater II (Species not determined).

230. Equatorial plate of spermatogonium, 19 chromosomes, x the odd one.

231. First spermatocyte, spireme stage.

232. First spermatocyte, prophase.

233. First spermatocyte, beginning of metakinesis.

234. First spermatocyte, equatorial plate, x the odd chromosome.

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

Ellychnia corrusca (Family Lampyridæ).

236. Equatorial plate of spermatogonium, 19 chromosomes.

N. M. S. del.

COLEOPTERA]

PLATE XIV.

Aphrophora quadrangularis (Hemiptera homoptera).

FIG. 237. Resting primary spermatogonium with lobed nucleus.

238. Resting secondary spermatogonium, with nucleus staining much more deeply.

239. Equatorial plate of secondary spermatogonium, 23 chromosomes.

240. First spermatocytes, very early growth stage, x the odd chromosome.

241-243. First spermatocyte, later spireme stages, showing the odd chromosome (x) and a pair of m-chromosomes (m).

244. Similar stage from a safranin-gentian preparation.

245. First spermatocyte, split-spireme stage, x the odd chromosome, m the m-chromosome tetrad.

246. Similar stage from a safranin-gentian preparation.

247-248. First spermatocyte, condensation of chromatin granules to form tetrads in the linin spireme.

249. Later tetrad stage.

250-251. First spermatocytes, metaphase from mercuro-nitric material.

252-254. Similar stages from Hermann material, showing longitudinal split in both the bivalents, and the odd chromosome (x).

255. First spermatocyte, anaphase.

256. First spermatocyte, telophase.

257. First spermatocyte, daughter plates containing 11 and 12 chromosomes, respectively.

258. First spermatocyte, a and c daughter plates, each containing 11 chromosomes, x the odd chromosome at a different level (b).

259. Second spermatocyte, equatorial plates of the two classes.

260. Second spermatocyte, metaphase.

261. Second spermatocyte, anaphase.

262-263. Second spermatocyte, daughter plates of the two classes.

N. M. S. del.

HEMIPTERA HOMOPTERA]

PLATE XV.

Aphrophora quadrangularis.

FIGS. 264-265. Second spermatocyte, telophase, showing chromatin nucleolus (n) and the products of division of the odd chromosome (x).

266. A spermatid containing the chromatin nucleolus (n).

267-268. Spermatids containing both the chromatin nucleolus (n) and the odd chromosome (x), a the acrosome.

269. Equatorial plate from a somatic cell of a male larva, 23 chromosomes.

270. Equatorial plate of an oögonium, 24 chromosomes.

271. Resting nucleus of a young oöcyte before synapsis, showing two pairs of condensed chromosomes, corresponding in size to the m-chromosomes and the odd chromosome of the spermatocytes.

272-277. Sections of nuclei of oöcytes, showing one or more of these heterochromosomes, from safranin-gentian preparations.

278-279. Bouquet stage from iron-hæmatoxylin preparations, showing the heterochromosome bivalent (x).

Cacoecia cerasivorana (Lepidoptera).

280. First spermatocyte, synizesis stage, showing 2 condensed chromosomes (x{1} and x{2}).

281-282. First spermatocyte, synapsis stage.

283-284. First spermatocyte, growth stages.

285. First spermatocyte, prophase.

286-287. First spermatocyte, later prophases, showing the heterochromosome pair (x).

288. First spermatocyte, metaphase.

289. Second spermatocyte, metaphase.

290. First spermatocyte, equatorial plate.

291-292. Second spermatocyte, equatorial plates.

Euvanessa antiopa (Lepidoptera).

293. First spermatocyte, equatorial plate.

N. M. S. del.

HEMIPTERA AND LEPIDOPTERA]