SPERMATOGENESIS IN PHILOSAMIA CYNTHIA. 99 



uneven contour. Several of the chromosomes are grouped 

 around a dark gray mass near the center of the nucleus, in which 

 I believe, from what occurs later, the plasmosome appears. 



The chromosomes seem to transform from rods, into longer 

 and thinner skein-like pieces, with rougher outline, and lighter 

 staining capacity. In Fig. 9 some of these pieces are seen to 

 form a spireme, and this, like the chromosomes in the preceding 

 figure, is centered around a large gray-staining mass, which is 

 seen in Fig. 10 to be a definite plasmosome. 



Spireme Stage. 



Figures 11, 12 are characteristic of the next definite stage. 

 The chromatin pieces now form a close intricately-coiled spi- 

 reme, the mass being contracted against one side of the nucleus, 

 nearest the greatest amount of cytoplasm, as Montgomery de- 

 scribed in Syrbtda. The spireme is not continuous, for several 

 free ends are seen in sections which give a complete focus of the 

 nuclei ; but it is impossible to determine the number of threads 

 which form it. A plasmosome is seen, entangled in the meshes 

 of the spireme. The threads are thicker and smoother in out- 

 line than in Fig. 9, and stain black even in sections which in 

 other respects are light in color. 



The question of synapsis was carefully studied in stages from 

 7 to 11, but I have not been able to obtain decisive evidence re- 

 garding the nature of the process. I was unable to find evidence 

 that the chromatin rods unite definitely two by two in forming 

 the spireme, but that they do unite in some manner seems clear. 

 Nowhere have I found stages which might be interpreted as par- 

 asynapsis, or side by side union of the chromosomes, such as has 

 been figured by the Schreiners, and other observers, nor could I 

 discover that in the spireme the threads show a longitudinal split. 



After contraction at one side of the nucleus, as shown in Figs. 

 11, 12, the spireme spreads out to occupy the entire nuclear 

 cavity, which increases in size. Fig. 1 3 represents an unusually 

 large nucleus, where the coiling of the threads, and the plasmo- 

 some, are distinctly seen. 



We may speak of this condition as the height of the spireme 

 stage. From this point onward, the spireme threads appear to 



