The Gametogenesis of Nepa Cinerea ( Water Scorpion). 241 
The nucleolus remains, becoming very large and staining deeply, 
whilst the disappearing threads stain more lightly, passing finally 
into the reticulate stage characteristic of the growth phase of the 
egg. Eapid growth takes place and yolk accumulates in the 
cytoplasm. In the case of the nurse and follicle cells thediplotene 
threads contract and break up in irregular masses of chromatin,, 
and distribute themselves about the nucleus, which does not 
increase in size. The nucleolus remains staining deeply, and the 
cells develop either into nurse cells, remaining in the nutritive 
chamber, or surround the oocyte as it passes down the tube, becom- 
ing follicle cells. Meantime the oocyte increases considerably in 
size owing to the deposition of yolk. Darkly staining particles 
appear in the yolk at this stage, and in a few preparations the 
emission of particles from the nucleolus and nucleus itself was 
noticed. The appearance of these particles in the cytoplasm marks 
the enormous increase in the size of the egg owing to yolk forma- 
tion. As the egg grows they break up into smaller ones and 
migrate to the edge of the egg, so that in the ripe egg these particles 
are collected round the border of the egg. By this time the 
nucleolus has considerably increased in size and does not stain 
uniformly, having lighter areas, giving it a vacuolar appearance. 
This is due possibly to internal changes. After the first extrusion 
noticed in the early stages nothing further happens, and hence it 
seems that the particles are thrown out by the nucleolus to 
stimulate the deposition of yolk. This interpretation has been 
applied to other types, and there seems no reason why such 
is not the case here. In fact the formation of yolk in the 
egg indicates a functional relationship between the nucleolus and 
the production of yolk, a conclusion many have reached after 
studying oogenesis in insects. A similar observation has been 
made by Browne in Notonecta as regards the behaviour of the 
nucleolus. It is described as the “ Karyosphere,” consisting of 
chromatic bodies embedded in plasmosome material, from observa- 
tions on the vesicular appearance during the growth period of the 
egg and formation of yolk and the increase in size of the primary 
spermatocyte, and further is supposed to supply the chromosomes 
with chromatin. However, the latter is questionable, for although 
in the male it appears attached in some cases, but not all, to the 
diplotene threads and is eventually unrecognizable, it persists in 
the female becoming very large in the growth stages, so that there 
is insufficient evidence to trace the supply of chromatin of the 
chromosomes to the nucleolus. 
Summary. 
1. Nuclear organization in the germ cells of Nepa cinerea has 
been investigated and compared with related types. 
