SPERMATOGENESIS IN PHILOSAMIA CYNTHIA. I05 



chromatin nucleolus is present, it is to be considered as a bivalent 

 body, arising by fusion or synapsis of the two idiochromosomes." 

 In Brochymena, however, they separate again before the first 

 division. 



I wish to acknowledge my indebtedness to Professor Cramp- 

 ton for suggestions and material and also to Professor Wilson for 

 kindly supervision and corrections, and reading of manuscript. 



Summary. 



1. The spermatogonia contain twenty-six chromosomes, of 

 approximately the same size and shape. 



2. There is a definite spireme stage with a simple plasmosome. 



3. The spireme segments into thirteen parts, of which twelve 

 form rings, the thirteenth becoming attached as a chromatin mass 

 to the plasmosome, which at this stage is double. 



4. In the growth period, when the twelve rings are definitely 

 formed, the chromatin mass is bent in a crescentic band around 

 the plasmosome, forming a chromosome nucleolus. 



5. This band represents a pair of idiochromosomes, and is 

 bivalent like the rings, but always appears as a single body. 



6. First and second metaphases show thirteen chromosomes. 

 Divisions are equal, so that the spermatids contain similar chromo- 

 some groups. 



Columbia University, 

 March, 1 907. 



LITERATURE. 



La Valette St. George 



'97 Zur Samen- und Eibildungbeim Seiden-spinner (Bombyx mori), Arch. Mikr. 

 Anat., 50. 



Meves, F. 



'07 Uber Centralkorper in mannlichen Geschlechtszellen von Schmetterlingen. 



Anat. Anzeig., 14. 

 Montgomery, T. H. 



'oo The Spermatogenesis of Peripatus (Peripatopsis) Balfouri up to the Formation 



of the Spermatid. Zool. Jahrb., 14. 

 '05 The Spermatogenesis of Syrbula and Lycosa, with general considerations upon 



Chromosome Reduction and the Heterochromosomes. Proc. Acad. Nat. Sci. 



Phil., Feb., 1905. 

 Munson, J. P. 



'06 Spermatogenesis of the Butterfly, Papilio Rutulus. Proc. Boston Soc. Nat. 



Hist., 33, no. 3. 



