STUDIES ON CHROMOSOMES 73 



DESCRIPTIVE 



Since the two species agree very closely save in respect to the 

 idiochromosomes they may conveniently be considered together. 

 Before describing the divisions, attention may be called to a 

 striking difference between the two species in respect to the size 

 of the cells and karyokinetic figures. As a comparison of the 

 figures will show, the spermatocytes and maturation division- 

 figures of N. hilaris are much larger than those of N. viridula. 

 In the spermatogonia this difference is also apparent, though less 

 marked. In the ovaries, strange to say, it cannot certainly be 

 detected, either in the dividing cells or in the nuclei of the follicle- 

 cells or of the tip-cells at the upper end of the ovary. It would be 

 interesting to make a more accurate study of these relations; 

 but I will here only state that the differences between the two 

 species seem to arise mainly through greater growth of the 

 spermatocytes in N. hilaris. With this is correlated a greater 

 size of the testis as a whole; but the size of the entire body in this 

 species is but little larger, as far as I have observed, than in N. 

 viridula. 



As regards the general features of the divisions, the diploid 

 groups of both sexes uniformly contain fourteen chromosomes, 

 the first spermatocyte-division eight and the second seven, the 

 idiochromosomes being, as is the rule in Hemiptera, separate and 

 univalent in the first division. 



1. The second spermatocyte-division 



a. The idiochromosomes. Polar views of the second division 

 always show 7 chromosomes which are usually grouped in an 

 irregular ring of six with the seventh near its center (fig. 3 j-m, 

 figs. 14, 15). In both species one chromosome of the outer ring 

 (s) can usually be distinguished as the smallest, though this is 

 not always evident owing to the apparent variations produced 

 by different degrees of elongation. This is the chromosome that 

 I formerly supposed to be the idiochromosome-bivalent, despite 

 its peripheral position, and despite the fact, which I had myself 

 described, that a similar small chromosome, also peripheral in posi- 



JOUHNAL OF MORPHOLOGT, VOL. 22, NO. I 



