STUDY OF CHROMOSOMES IN NOTONECTA 127 



ones is well shown in figure 41, where these four chromosomes 

 happen to lie together. 



The inequality in the X and Y chromosomes is quite striking 

 in most cases in N. glauca, but is not so great as in the species 

 previously described. There seems to be some individual vari- 

 ation in this respect, the XY pairs from one individual (fig. 42) 

 being more nearly equal than in another (fig. 43). This varia- 

 tion is more marked in N. shooterii, in connection with which the 

 question is discussed more fully. I have found no case in N. 

 glauca in which I have been unable to detect an inequality. 

 This species resembles Nezara hilaris (Wilson '11) in having a 

 constant but often slight difference in the components of this 

 pair, although this difference is perhaps greater in N. glauca. 

 In anaphase, X and Y pass to opposite poles and also the sister 

 elements of the two large chromosomes which at this time are 

 less characteristic in shape (fig. 44). In the late anaphase (figs. 

 45 and 46) these chromosomes are noticeable as long, somewhat 

 curved bars, and sometimes the larger one gives the appearance 

 of being double on account of a notch in the center, a remnant 

 possibly of the bend in the original U which was one of the four 

 parts composing the large chromosome. Sister anaphase groups 

 in polar view are practically identical except for the central chro- 

 mosomes which differ in size, sometimes considerably (fig. 47), 

 sometimes less noticeably (fig. 48). Owing to this fact of course, 

 the spermatids and likewise the spermatozoa will be of two kinds 

 with regard to their chromatin content, bearing the usual relation 

 to sex-production. 



The growth of the cells in N. glauca is very slow, as has been 

 noted also by Pantel and Sinety, and on this account most of 

 the cysts containing spermatogonia and early growth stages are 

 empty at the time that the division stages occur, so that few di- 

 viding spermatogonia are to be found in the material used for 

 the maturation divisions. The best one occurring in my mate- 

 rial is shown in figure 49, and although the number cannot be 

 counted with certainty, the group shows the structure of the 

 two largest chromosomes which appear as long curved rods. 

 This figure also shows the presence of four small chromosomes 



