No. 2.] ANURIDA MARITIMA. 225 
of nucleoli. These masses vary in number from one to two. 
The cell bodies of the nutritive cells have increased greatly in 
size, and at this stage show the differentiation into two kinds 
of material most clearly. By the use of lithium carmine and 
Lyon’s blue the contrast is rendered most vivid. The chromo- 
somes and nucleoli stain a brilliant red in the carmine, differ- 
entiating the nucleolus as a peculiarly refractive body. The 
cell body protoplasm stains a rather purplish red, being affected 
to a slight degree by both stains. Thecap of different material 
comes out a brilliant blue, as also does the yolk present in the 
protoplasmic meshes of the ovum. Although no membrane 
can be found delimiting this blue material, its edge is as clear 
cut as if such a condition existed. From the constantly circu- 
lar appearance of the nuclei of the nutritive cells when cut in 
all planes it is evident that they are spherical, and hence the 
blue material must cover the nuclei as a cap on the side facing 
the egg, thus causing the nucleus to take an eccentric position. 
While these changes are taking place in the ova and nutritive 
cells the wall of the ovary begins to grow round each of the 
cell masses, and finally the ovum and the cells that contribute 
to its formation are inclosed together in a more or less com- 
pletely separate sac (Fig. 4, f.). During the period of yolk 
formation the follicle is gradually stretched more and more, 
and hence becomes thinner and thinner. Thereis no evidence 
that the follicular cells divide either kinetically or akinetically, 
as has been described by Wheeler (89) in Doryphora and 
Blatta. This thinning process is continued until, as shown in 
Figs. 11 and 12, the follicle is hardly distinguishable. At no 
time is it a prominent feature of the ovary, and it becomes 
more and more insignificant from the beginning of yolk forma- 
tion. Its slight development isa most potent argument against 
its taking any active part in yolk formation. Commonly the 
follicular cells either completely or in part supply the elements 
of this process. In many cases, as shown by Stuhlmann 
(86) and others, a highly developed follicle is present; also 
an ovarian wall and nutritive cells. As a rule, however, the 
degrees of the development of the follicle and the nutritive 
cells stand in inverse ratios, the work of aiding the egg in 
