STUDIES ON CHROMOSOMES 83 



4. The diploid chromosome-groups 



In these groups the interest centers again in the identity of the 

 idiochromosomes and the d-chromosome. Of the 14 separate 

 chrosomomes present in the diploid nuclei of both sexes, none 

 shows any constant indication of duality (figs. 4 a-h). The d- 

 chromosome can not, therefore, be identified in these stages. 

 Secondly, in both species the diploid groups of the two sexes show 

 the same relation as in other Hemiptera of this type, though this 

 is, of course, more readily seen in N. viridula than in hilaris, owing 

 to the small size of the Y-chromosome. In the spermatogonial 

 groups of this species (4 c, d) this chromosome is at once recog- 

 nizable while in the female groups (g, ti) it is lacking, its place 

 being taken by one of larger size. In both sexes the small pair 

 (s, s) is also recognizable. In this species, accordingly, the Y- 

 chromosome is confined to the male line, and the Y-class of 

 spermatozoa must be male-producing, as in other forms. 



In N. hilaris the Y-chromosome can not be identified (4 a, 6), 

 but the relation of the spermatozoa to sex-production is shown in 

 another way, though less unmistakably than in N. viridula. As 

 already described, the large idiochromosome or X-chromosome is 

 one of the largest three chromosomes seen in the second division. 

 We should therefore expect to see five largest chromosomes in 

 the male diploid groups. This is clearly apparent in figs. 4 a, 6, 

 and is also shown in the corresponding figures of N. viridula 

 (c, d) though not quite so clearly. One of these five in the male 

 should be the X-chromosome; and if the usual relation of the 

 spermatozoa to sex hold true, there should be six largest chro- 

 mosomes in the diploid groups of the female. This relation actu- 

 ally appears in nearly all cases, and is shown in figs. 4 e, f, g, h, in 

 each of which, again, the small pair (s, s) may be recognized. 

 Though this evidence is in itself less convincing than that afforded 

 by N. viridula (since the relation can not always be made out 

 with certainty) it is fully in harmony with the latter, and sustains 

 the same conclusion. 5 



5 This relation is shown in my original figures of N. hilaris, though not quite 

 as clearly as in the groups here figured. In my first 'Study' ('05) the five largest 

 chromosomes are very clearly shown in fig. 4 h, and are also evident in 4 q. In the 

 third 'Study' the relation is hardly evident in the male but fairly so in the 

 female (figs. 5 I, TO). 



