1910.] NATURAL SCIENCES OF PHILADELPHIA. 301 



observation of the division in autumn of a few first spermatocytes of 

 P. cynthia and her suggestion that these degenerating cysts of cells can 

 be traced to the degeneration of those cells which have undergone 

 precocious maturation seems an excellent explanation of their origin. 



Next to these synapsis and synizesis stages and arranged in some 

 sort of sequence from the periphery to the center of the cysts are found 

 ■spermatocytes in various stages of growth; primary spermatocytes, 

 secondary spermatocytes, spermatids, and developing and developed 

 spermatozoa. 

 Callosamia promethea. 



1. Spermatogonia. — The spermatogonia of promethea are small oval 

 cells which in their earlier stages are crowded together and closely 

 pressed against the walls of the testes. Secondary spermatogonia are 

 somewhat larger and extend further inward so that they are easily 

 studied. In what Wilson (1902) says has been falsely characterized as 

 ""the resting stage", the nuclei are spherical and faintly staining and 

 fill by far the greater part of the cell ; within the nucleus is found an irreg- 

 ular meshwork of linin threads upon which chromatin granules are scat- 

 tered. In the early spermatogonial cells (PI. XXII, figs. 1 , 2 and 3) there 

 ■are found chromatic masses or "net knots" : they are spherical and re- 

 semble plasmosomes in which chromatin granules are entangled. These 

 granules are of the same size as those scattered throughout the nucleus, 

 and that they are simply an aggregation of these is suggested by the 

 fact that in later stages, when the granules are more widely scattered 

 through the nucleus, this net knot, after decreasing in size and in the 

 number of contained granules, finally disappears (fig. 4). The basi- 

 chromatin granules now stain more deeply and become aggregated 

 along the linin to form a spireme. It has been impossible in C. prome- 

 thea to distinguish any structure in this spireme, though in smear prep- 

 arations of P. cynthia it is clearly seen to be composed of twenty-six 

 pairs of chromosomes lying side by side and each joined to the other by 

 linin threads. The significance of this will be discussed later. The 

 chromatin of the spireme condenses, and in equatorial plates of the 

 last spermatogonial division thirty-eight small, densely stained, and 

 compact chromosomes may be made out (fig 6). In smear preparations 

 this plate is easily seen, and among the chromosomes one pair is very 

 plainly smaller than all the others ; but even here, where the size of the 

 plate is enlarged many times by the method of fixation, it is still too 

 small to offer much opportunity for studying size relations. 



In preparation for the last spermatogonial division the chromosomes 

 become regularly arranged upon the spindles, divide equally and are 



