GAMETOGENESIS IN PHILOSAMIA CYNTHIA. 41 



in the second division. Thus the two polar bodies receive groups 

 exactly like that of the egg. 



At the time of fusion of the germ nuclei, just before the nuclear 

 walls break down, 13 chromosomes may be counted in the female 

 pronucleus, 13 in the male pronucleus, this being the number 

 found in the spermatocytes. By fusion of the two groups, the 

 somatic number is obtained, which is found in the ensuing 

 embryonic divisions. 



Thus on the basis of observable differences in chromosomes, 

 there is no indication of a nuclear dimorphism in the eggs, nor 

 of the presence of idiochromosomes. 



In the papers on spermatogenesis of Lepidoptera, above re- 

 ferred to, the writers describe a dumb-bell-shaped body, which is 

 distinguished from the other chromosomes by its condensed form 

 during growth. Later it becomes indistinguishable from the 

 other chromosomes, and divides normally. This has been inter- 

 preted as an idiochromosome in which the X and Y elements are 

 equal. Thus the Lepidoptera, as has been previously suggested, 

 appear to belong in the same class with Nezara, which possesses 

 an equal pair of idiochromosomes in the male. If the spermato- 

 zoa are to be considered dimorphic, it is necessary to assume 

 a qualitative difference between X and F. However the facts 

 may be interpreted, there is no essential disagreement between 

 gametogenesis in cynthia and in other insects in which no nuclear 

 differences are observable. 



March, 1912. 



LITERATURE LIST. 

 Cook, M. H. 



'10 Spermatogenesis in Lepidoptera. Proc. Acad. Nat. Sci. Phila., April. 

 Dederer, P. H. 



'07 Spermatogenesis in Philosamia Cynthia. Biol. Bull., XIII., 2. 

 Morrill, C. V. 



'10 The Chromosomes in the Oogenesis, Fertilization and Cleavage of Coreid 



Hemiptera. Biol. Bull., XIX., 2. 

 Stevens, N. M. 



'05 Studiesin Spermatogenesis. I. -II. A Comparative Study of the Hetero- 

 chromosomes in Certain Species of Coleoptera, Hemiptera, and Lepidoptera, 

 with Especial Reference to Sex Determination. Carnegie Inst. Publicat. 

 No. 36, II. 



