N. M. Stevens

“ 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. ”

“ In both an even number of chromosomes (22, 18) was found in the spermatogonia, [Pg 45] one being very small and forming with a larger one an unequal pair which remained condensed during the growth stage and separated into its larger and smaller components in the first spermatocyte mitosis. The result of maturation, as in the other species here described and in Tenebrio molitor, is dimorphism of the spermatozoa. The method of synapsis in Coptocycla is like that described for Chelymorpha argus. ”

“ Figures 32 and 33 are prophases of the second division, figure 33 showing the small chromosome ready for metakinesis. It was impossible here also to get good drawings of daughter plates of the second spermatocytes to show the content of the two classes of spermatozoa, but there is no doubt that all of the chromosomes divide in the second mitosis, giving one class of spermatids containing the small chromosome, the other class its larger homologue.
No male somatic cells were found in mitosis, but they would, if found, show the same conditions as in the spermatogonia. ”

“ Figures 50 and 51 show polar views of the metaphase, the smaller element (x) being the unequal pair. The chromosomes in late anaphase are too much crowded to give clear drawings. As in all the beetles so far studied there is no rest stage between the two maturation divisions, but the late anaphase of the first mitosis passes over quickly into the second spindle. ”

“ The larvæ only were collected, as they gave all the desired stages for a study of the spermatogenesis, and also oögonia and synizesis and synapsis stages of the oöcytes. In the first collections the testes were dissected out, but the many free follicles break apart so easily that the later material was prepared by cutting out the abdominal segments which contained the reproductive organs, and fixing those without dissection. The same methods of fixation and staining were employed as for the Coleoptera. ”

“ The spindle in prophase (fig. 68) is much elongated and the 8 chromosomes are often spread out upon it so as to be easily counted. In the early metaphase the parachute-like heterochromosome group is always nearer one pole of the spindle (plate X, figs. 69 and 70) . The equatorial plate often shows both the larger component of the pair and the plasmosome (fig. 71) . Figures 72-74 show the metakinesis of the heterochromosome bivalent. In figure 74 the two unequal elements are completely separated and the plasmosome has disappeared. ”

“ The very young follicles are spherical, the older ones ovoid in form. The primary spermatogonia (plate XIV, fig. 237) —very clear cells with a lobed nucleus which stains slightly—occupy the tip of the follicle. Next to these comes a layer of cysts of secondary spermatogonia which are conspicuous for their deeper staining quality (fig. 238) . There appears to be no plasmosome in either class of spermatogonia. Figure 239 is the equatorial plate of a secondary spermatogonium. There are 23 chromosomes, two of which are conspicuously larger than the others and evidently form a pair. ”

“ 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. ”

“ 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. ”

“ The dumb-bells are so bent at the ends (fig. 52) that the spindle fibers, here also, are attached at or near the center of each univalent component of a bivalent chromosome, and the separated, univalent chromosomes go to the poles of the spindle in the form of Vs. As in Tenebrio the heterochromosome pair is late about coming into the equatorial plate (figs. 47-48) , but it does finally take its position with the others (fig. 49) and separates into its component parts somewhat earlier than the other bivalents (figs. 52, 53) . ”

“ Sections of male pupæ were examined for equatorial plates of somatic mitoses. Figure 1 is a specimen of such plates. As might be expected, this figure resembles quite closely the spermatogonial equatorial plate (fig. 3) in number, form, and size of chromosomes, the small one being present in both. ”

“ Here Morgan's ('06) suggestion as to degenerate males seems much to the point. The male sex [Pg 56] character, having become dominant in certain eggs at an early stage, may, from that time on, determine the kind of development. ”

“ 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. ”