A (’oniparative Study of the Chromosomes etc. 
255 
chromosomes, but also in actual size'^). The large pair (ili) is present in 
both species. The one great difference in the spermatogonia is the pre- 
sence of eighteen small chromosomes in E. binotota as compared with 
seventeen in E. curvata. From a study of the maturation divisions of 
E. curvata, we know that one of the seventeen is an unpaired Z-chromo- 
some. In E. binotota, on the contrary, we have ten bivalent chromo- 
somes in both maturation mitoses, none of which are composed of asym- 
nietrical halves. We ai'e therefore led to the conclusion that, if any 
sex chromosomes are present in E. binotota, they must be paired and 
equal in size. This would be contrary to all cases so far reported among 
the Homoptera, and only one such case, that of Oncopeltus (Montgomery, 
’Ol, ’06; Wilson, ’lla), remains among the Heteroptera, since Wilson 
(’lOa, ’lla) has found his former description of Nezara {'Odai) to be in- 
correct. Montgoihery (’06) claimed that the idiochromosomes of Nezara 
hilaris were of unequal size. In the Heteroptera the components of the 
idiochromosome pair iisually remain separate in the first maturation 
division and pair only in the second division. This gives a clew to the 
presence of definite sex chromosomes, which are usually unequal in size. 
Since the maturation mitoses afford no evidence which enables us to 
deterniine the presence of definite sex chromosomes in the spermatogonia 
of E. binotata, we are left entirely to the study of the growth period of 
the spermatocytes for any facts which may lead us to believe that they 
are present. 
VII. Growth Period of Spermatocytes. 
A. Enchenopa binotata. 
After the last spermatogonial division, the autosomes can not be 
followed directly as individuals through the various stages leading up 
to the formation of the leptotene threads. The nuclei of the early sper- 
niatocytes are characterized by a very fine network, along which the 
chromatin granules are scattered. At the points where the fibers forming 
the network unite, the chromatin forms larger masses, which give the 
nucleus a characteristic dotted appearance (Plate XIX, Fig. 45). The uet- 
4) It is of utmost importance, in making comparisons of the size and shape of 
chromosomes in different species to use material which has been fixed and stained in 
exactly the same way. Thus Figure 36 (Plate XIX) represents a spermatogonium of E. 
ciirvaia from a testis killed in Bouin’s fluid. While the chromosomes are clear and 
distinct, yet they differ greatly from those killed in Hermaxx’s fluid (E. curvata, Figs. 32 
to 35; E. binotata, Figs. 20 — 23), being more angidar and ha\nng the curvatme of the 
macrochromosomes increased. 
ArchiT f. ZellforscLung. XII. 
17 
