104 M. Ussow’s Zoologico-Embryological Investigations. 
it acquires the form of a very flat, conical disk, in the thick- 
ened central part of which the germinal vesicle is situated. 
The above-described folds of the granulosa are gradually 
effaced as the ovum enlarges, and finally disappear alto- 
gether, so that at last it becomes perfectly smooth both within 
and without. The perfectly mature ovum by its own weight 
ruptures the very thin part of the envelope (the so-called 
stigma) at the upper pole, and is fecundated* at the moment 
when it falls into the ventral cavity (Argonauta). — 
For the elucidation of the above-mentioned question as to 
the continual development of the ova of Cephalopoda com- 
mencing at different times, I may add that I have succeeded 
in observing that, at the time of the strongest development of 
the folds, new ova are developed im the Graafian follicle from 
any of the cells of the epithelial membrane. A part of the 
inner surface of the fold gradually covers the newly formed 
ovum, which during its enlargement protrudes at the surface, 
becomes constricted off from the Graafian folliele, and finally 
remains united to the theca folliculi only by means of a short 
peduncle. Thus, in consequence of more or less copious 
nutrition, the cells of the granulosa of a Graafian follicle may 
in a short lapse of time bring the primitive ovicell to full de- 
velopment, and secrete the whole mass of the nutritive vitellus 
and finally the transparent choriont. ‘This is in its main 
features the mode of formation of the Graafian follicle and 
the ova of the Cephalopoda. Of its correctness I am perfectly 
convinced by an attentive and frequently repeated study of 
the process. As regards the original development of the 
female sexual organs of the Cephalopoda, I could not trace it, 
as it appears to be correct that the mature embryo, after 
its escape from the egg, and even the young animal from one 
to three days old, possess no trace of these organs} ; but at the 
end of three days, during which it has used up the whole of 
the outer and a part of the inner nutritive vitellus, the animal 
dies, and consequently deprives us of all possibility of inves- 
tigating the development of the sexual organs and the part 
taken by the germ-lamelle in their construction. With 
* I can assert this positively with regard to the fecundation of Argo- 
nauta. Although in all the other species, also, I found perfectly mature 
spermatophora in the ovaries, the segmentation takes place always outside 
the body, which would indicate a pause between the fecundation and the 
commencement of development. 
+ In Argonauta also the longer or shorter filiform process. 
} The same results were obtained also by Kolliker (/. ¢. p. 110) and 
Metschnikoff (7. c. p. 65). At the end of the third period I have observed 
helow the ventricle in Sepia and Loligo an aggregation of cells, from 
which it is possible the sexual organs are developed. 
