180 The Spermatogenesis of Abraxas 



Since it is in the egg that the incompatibility between the sex 

 determinant and a body character is found, logically it is in the 

 maturation of the egg that the chromosome which determines this 

 character, if it exists, should be sought. But the practical difficulties 

 in studying the maturation of an egg provided with a thick shell are 

 so great that the spermatogenesis was investigated first, in order to 

 find out whether any differences exist between the chromosome groups 

 in the pure forms of the two varieties, and in the heterozygote produced 

 by crossing them. 



The spermatogenesis lasts for a considerable period in the late larval 

 and early pupal stages ; during the first week or so of pupal life all 

 stages may be found from spermatogonia with division-figures, through 

 growth stages to spermatocytes with first and second divisions, and the 

 conversion of the spermatids into spermatozoa. The testes are divided 

 into several compartments, each containing numerous follicles, and 

 within these compartments at one end or side spermatogonia are 

 found, and from these the later stages may be traced in fairly regular 

 order, all the cells in one follicle being at nearly the same stage. The 

 male and female pupae can be distinguished by the pits representing 

 the genital openings of the moth, and the material was prepared by 

 opening male pupae in Ringer's fluid (NaCl 0'7 gr., CaClj 0*23 gr,, 

 KCl 0"3 gr.. Water 1000 c.c), removing the orange-coloured testes 

 which are united in the middle dorsal line, and fixing them for about 

 half to one hour in Flemming's strong fluid. After being well washed 

 in water, and taken gradually through successive alcohols into cedar 

 oil, they were embedded in paraffin and cut into sections 6/i in 

 thickness. They were stained on the slide with Heidenhain's Iron 

 Haematoxylin. Testes of larvae were also examined in the same way. 



The spermatogonia are rather small, and not so clearly divided into 

 follicles as in the later stages. Some follicles or groups of cells show 

 mitoses, in which the chromosomes form a flat equatorial plate and 

 very regular anaphase figures, but the chromosomes are so small and 

 numerous that I have not been able to count them with complete 

 accuracy. The number however is clearly at least 50 (Fig. 1), and 

 a study of the later divisions makes it probable that it is in reality 5G. 



After the last spermatogonial division the nuclei undergo a growth 

 stage, during part of which the chromatin takes the form of a great 

 number of fine granules almost filling the nucleus. Some groups of 

 cells among the spermatogonia occasionally degenerate, and produce 

 masses of deeply staining material. As growth proceeds, the normal 



