1910.] NATURAL SCIENCES OP PHILADELPHIA. 313 



stages of the last spermatogonial division; here the chromosomes in 

 metaphase are too crowded to count. A thin skein is formed prepara- 

 tory to synapsis (fig. 143) and by condensation of this the chromatin 

 becomes collected at one side of the nucleus (fig. 144); later it spreads 

 through the nucleus and gradually fills it (figs. 145 and 146). In the 

 growth stage which follows we find the same large, deeply-staining 

 body described for the other species. The centrosomes which have 

 been followed since the last division of the spermatogonia are seen 

 at this time as two small dark bodies near the nuclear membrane 

 (fig. 147); these may be clearly seen to pass through the regular 

 cycle of changes, a cycle which is repeated in each maturation division, 

 and which in many respects may be parallel with the changes which 

 take place during division of the nucleus. In S. cecropia, as in all 

 the other species here studied, the centrosomes seem to be continuous 

 from generation to generation as is the nucleus itself. The chromo- 

 somes, in smear perparations, retain their outlines during the growth 

 stage (fig. 148); in this the nucleus has been separated from the cyto- 

 plasm and much stretched in drying. Corresponding almost exactly 

 with similar stages in C. promethea, we have the gradual condensation 

 into rings and dumbbells, while the idiochromosome, which retains 

 its continuity longest, finally assumes the same form as the others and 

 is indistinguishable from them. Division in first and second matura- 

 tions closely follows that of the other Saturnids, and the remnants of 

 the spindle fibers which surround the chromosomes of the last division 

 and extend far into the cell cytoplasm may be seen to go directly into 

 the spermatid and there form the nebenkern. The spermatozoon has 

 here been traced to its complete development. The earlier stages 

 correspond to those described for other members of the family, but 

 as development proceeds (PL XXVII, figs. 167-170), the decrease in size 

 of the nucleus and elongation of the tail seem to be connected with the 

 extension of the head piece, which at this time appears as a cytoplasmic 

 projection containing a darker body and only differing from the rest 

 of the cytoplasm in its greater clearness. While the chromatin has 

 been condensed into a small round mass which completely fills the 

 nucleus, the head piece has increased in length and has become pointed 

 and shield shaped, and the axial filament has grown very long. The 

 final stage of development shows a pointed head piece with its acro- 

 blast, a long narrow nucleus, a very slightly developed middle piece, 

 and an exceedingly long tail which, due to a twisting of the inner and 

 outer membranes about the axial filament, has the appearance of a 

 spiral. 



