242 
Transactions of the Society. 
2. The diploid complex in male germ cells consists of thirty- 
five chromosomes of various sizes, that of the female thirty-six. 
3. The maturation stages are typical, with definite polarization 
of threads. 
4. There is a single X-chromosome in the male and a pair in 
the female, but they are not conspicuous, and unable to be identified 
until division takes place. This differs from Notonecta and 
Ranatra, which have an XY-group. 
5. The X-chromosome converges to one pole either before or 
behind the autosomes in the first division, and divides equationally 
in the second. This is confirmed by haploid numbers seventeen 
and eighteen of the secondary spermatocytes. Notonecta and 
Ranatra separate in the second division. 
6. The differentiation of the oocytes, nurse cells and follicle 
cells does not take place till after synapsis. 
7. The ejection of particles from the egg nucleus iu the growth 
stage coincides with the deposition of yolk. 
8. The nucleolus is conspicuous throughout all the oocyte 
stages and up to the diplotene in the male. It consists of 
chromatic bodies embedded in plasmosome material, the amount 
of each varying with the stages. 
9. There are marked differences between Nepa cinerea and 
Ranatra and also Notonecta, notably the diploid complex, the 
XY-group, the separation of X in the first instead of the second 
divisions, and as regards the former only there is no polymorphism 
of the spermatocytes. 
10. There is similarity in the presence and behaviour of the 
nucleolus and the appearance of the diplotene threads in ring 
formations. 
11. There is a difference with other members of the group 
Hemiptera in the orientation of the maturation figures, and the 
reduction of X-chromosome in first and not second division. 
This investigation was carried out at Birkbeck College. I am 
greatly indebted to Dr. Hogben for the preparations he gave me 
to carry on the w T ork, and further for helpful advice and suggestions 
throughout. 
References. 
Browne, E. N. — Study of Male Cells of Notonecta. Journ. of Exper. Zool., 
No. 14. 
Study of Chromosomes of Notonecta. Journ. of Morph., xxvii. 
Chromosome Number and Species in Notonecta. Biol. Bull., xx. 
Chickering. — Trans. Amer. Micro. Soc., xxxvii. (1918). 
Hogben, L. T.-*-Studies in Synapsis, II. and III. Proc. Roy. Soc., xci. 
and xcii. 
Montgomery. — Chromosomes in Spermatogenesis of Hemiptera. Trans. 
Amer. Phil. Soc., xxi. 
Wilson, E. B. — Studies on Chromosomes, III. and VIII. Journ. of Exper.- 
Zool., Nos. 8 and 18. 
