SPERMATOGENESIS IN PHILOSAMIA CYNTHIA. IOI 



There is a very constant difference in the appearance of the two 

 parts of the plasmosome. One half is clear and transparent, the 

 other, slightly granular, and stains a deeper gray. Various views 

 of it are shown in Fig. 19, a to e, drawn from nuclei of the same 

 stage as Fig. 18. Three side views are given in Fig. 19, a—c ; in 

 the two latter the gray half seems more darkly granular at its 

 region of union with the other. In end view, d, e, only one part 

 is seen in outline, so that the structure appears as a single sphere, 

 but a smaller granular area is found in the center, which seems to 

 be nothing but the granular region indicated in b, seen through 

 the clear half of the plasmosome. 



The intervening history from the breaking up of the spireme 

 into thirteen elements, and the appearance of a double plasmo- 

 some, up through the stage when rings are formed in the growth 

 period, will be passed over for the present, to a consideration of 



the 



Maturation Divisions. 



In prophase of the first maturation division, the chromosomes 

 appear regularly bipartite, and approximately equal in size (Fig. 

 30), placed irregularly upon the spindle, in preparation for meta- 

 phase. (The section lacks two of the typical number.) Many 

 very clear metaphase groups, seen in polar view, show invariably 

 thirteen chromosomes. Two incomplete sections (Figs. 33, 34) 

 give views of typical anaphases, where division always appears 

 equal. 



Polar views of the second metaphase (Figs. 36, 37) have the 

 same grouping and appearance as in the first division, the only 

 difference being in the size of the chromosomes. In a late 

 anaphase of second division (Fig. 38), the chromosomes of each 

 group are approximately similar in size, and in none of the ana- 

 phases studied have I seen a case of unequal division. In early 

 telophase the chromosomes are crowded together, and difficult 

 to count, but several counts from polar view, or slightly oblique, 

 showed the usual number, thirteen. Figures 39-41 are various 

 views, all showing thirteen chromosomes as a result of second 

 division. Fig. 42 shows the characteristic lengthening of the 

 spindle in this division. 



From the foregoing facts it is clear that in Philosamia there is 



