Studies on Chromosomes 13 



The sister groups are practically exact duplicates save for the 

 heterotropic which varies considerably in appearance as seen from 

 the pole owing to foreshortening (cf. the side-views given in my 

 preceding paper). The spermatogonia correspondingly show 

 always thirteen chromosomes (Fig. 3, <?), of which the largest and 

 the smallest pair are at once distinguishable. Next follow four 

 chromosomes nearly equal in size, two of them often appreciably 

 smaller than the other two. Of the remaining five, one must be 

 the unpaired heterotropic; but, as already stated, it cannot be 

 positively identified by inspection. Closely similar groups may 



^^ m 



4a* ** 



ft*. 



a 



k 



. 



c ? d f 



J 



FIGURE 3 



Alydus pilosulus. a, Spermatogonial group; b, group from a dividing investing cell of the testis; 

 c, oogonial group; d, from a dividing cell of an egg-follicle; e, f, two pairs of sister-groups, each from a 

 single spindle, anaphase of second spermatocyte-division, in polar view. 



occasionally be found in dividing cells of the enveloping cells of 

 the testis (Fig. 3, &). Whether multiple groups occur like those 

 described in Anasa, I cannot say. 



The dividing oogonia and follicle-cells, of which a large number 

 have been observed, always show fourteen chromosomes that may 

 be arranged in seven equal pairs (Fig. 3, c, d}. As in the sper- 

 matogonia, the largest and the smallest pair are usually at once 

 recognizable, and also the four second largest. The remaining 

 six, of nearly equal size, must of course include the heterotropic 

 chromosome and its maternal mate. 



