232 
W. M. Wheeler 
Stage 3. 0.275 mm long. This Stage sliows a slight advance 
beyond tlie precediug. A small cavity — the first trace of the body- 
cavity, which probably exists in 'potentia before this stage — makes 
its appearance as a small space surroimdiDg the ovary. It probably 
arises by a Separation of the dorsal and ventral layers of the peri- 
toneal epithelium. These two layers have probably become closely 
applied to each other through the rapid growth of the parenchyma 
in the dorsal and ventral extraperitoneal regions of the body. 
The general appearance of the ovary is that of the precediiig 
Stage, but at its periphery a few of the cells tend to detach them- 
selves from the greater mass and to fall into the incipient body-cavity. 
When closely studied, these loosened cells prove to be in reality 
small cell-clusters , each consisting of a larger and clearer oocyte j 
and two accessory cells. The latter are closely applied and, as it 
were, moulded to the roimded surfaces of the oocyte. When two i 
accessory cells are present they iisually lie on opposite surfaces of 
the oocyte, but they may lie side by side on adjacent surfaces. When ; 
this latter arrangement obtains the series of 3 cells forms an angle, 
so that it is often possible to see but one accessory cell, the other , 
being concealed by the oocyte. Perhaps in certain cases only one 
accessory cell is present. In this third stage there are no mature 
spermatozoa, though the testes are more voluminous than in preceding 
stages and contain many dividing spermatogonia and spermatocytes. ' 
Stage 4. 0.3 mm long. The gut-diverticula have lengthened 
somewhat; the body-cavity has extended itself laterally from the 
ovary and over each intestinal lamification. Within this body-cavity i 
it was possible to observe a few free oocytes with their accessory 
cells evidently moving away from the ovary. 
Besides the dividing spermatogonia and spermatocytes many 
developing spermatids and a few quite mature spermatozoa were i 
found in the parenchyma ventral to the intestine. 
Stage 5. 0.35 mm long (PI. 10 Figs. 16 and 17). In this 
stage the intestinal branches have leugthened and the superjacent 
diverticula of the body-cavity [coe] are coextensive with or even 
exceed the intestinal branches in length. The ovaries still consist 
of a single pair of flattened cell-masses. Figs. 16 and 17 represent 
two successive sections — the former passing through the body of 
the ovary, the latter grazing its posterior end. The oocytes with 
their accessory cells [o.m] are seen swimming in the body-cavity. 
A few have already apparently attached themselves to the peritoneal 
