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W. M. Wheeler 
anterior edges of their backs. These smaller individuals have been 
rightly regarded by v. Graff and others as the young of the same 
species. Beakd’s observations on these yonng, wbich it pleases him 
to call »complemental males«, will be considered in tke sequel. 
Here I am concerned only with an account and interpretation of my 
own observations. 
The ovaries oi M. glabrum are a single pair of deeply staining 
oval masses, one on either side of the intestine in the middle of 
the body. In horizontal sections the general appearance of these 
Organs is that of PI. 10 Fig. 20 ov. Fach mass is not solid like an 
evary of M. cirriferum^ but permeated with narrow and irregulär 
spaces. The true relations of the ovaries to the body-cavity and 
circumjacent organs are best studied in transverse sections (Fig. 19). : 
The ovaries are seen to consist of deeply staining cavernous invagi- ' 
nations of the uterine wall on either side of the intestine. The 1 
spaces which permeate them are continuous with .the lumen of the 
Uterus [iit] and its ramifications, the main branches of the »ovaries« , 
of other authors. The minute structure of an ovary is shown in 
Fig. 21. In this tigure it is readily seen that the organ is really a 
sudden and pronounced thickening of the peritoneal epithelium ['p.ep) \ 
lining the »uterus« (body-cavity) and its ramifications. The thickening i 
takes on the appearance of an invagination because its central por- 
tions are traversed by the spaces above described. These spaces, as 
will be seen, probably arise by the breaking away of cells in certain 
portions of the ovarian mass. The organ clearly consists bf two kinds < 
of cells, the larger and paler elements being oogonia or oocytes, ; 
the smaller and more deeply staining elements the accessory .cells. i 
In the specimen tigured a number of spermatozoa [sp] have migrated 1 
from the body-cavity into the ovarian crypts. In the ovaries of inany : 
specimens — especially during the younger stages — the oogonia may 
be seen dividing. I have reproduced several such cells in Fig. 22. 
It will be observed that the accessory cells are already attached to 
the dividing oogonia. The divisions are evidently about to result 
in the formation of more oogonia or oocytes. I have not been able 
to determine how these new oogonia or oocytes acquire their accessory 
cells — whether by a division of the original accessory cells, or 
by attracting to their surfaces some of the deeply staining cells 
which occur so abundantly in all parts of the ovary. The solution 
of this Problem is by no means easy, for not only are all the cells 
of the ovary yery small and closely applied to one another, but the 
