M. Ussow’s Zoologico-Embryological Investigations. 105 
regard to the spawning-time*, the number of mature ova and 
other details in the formation and development of the Graafian 
follicle and other accessory glandular organs (albumen- or 
nidimental glands of the Cephalopoda), I reserve their de- 
scription for a complete memoir on the animals named. 
If. Segmentation of the ova of the Cephalopoda, and forma- 
tion of the one-layered germ (blastoderm). 
The whole of the mature ova which fall from the Graafian 
follicles into the ventral cavity are, apparently, without ex- 
ception, fecundatedt. The mature Cephalopod ovum, which, 
in form, is very like a hen’s egg, contains the following 
parts :—1, a very small mass of the so-called formative vitellus, 
which, as we have seen, represents the finely granular proto- 
plasm of the primitive ovicell with its nucleus (germinal 
vesicle) ; 2, a greater or less quantity of the rather viscous, 
fatty nutritive vitellus; 3, a perfectly transparent albuminous 
substance which occupies the space between the vitellus and, 
4, the many-layered vitelline membrane (chorion) with its 
tubuliform micropyle; and, lastly, 5, a more or less thick, 
many-layered egg-capsule which sometimes runs out into an 
elastic thread, serving to attach the ova to various objects 
under water (Argonauta}, Sepia), and sometimes forms a 
longer or shorter sac containing 10-100 or more ova (Sepiola, 
Loligo). 
At the moment of fecundation the germinal vescicle does 
not disappear; and the segmentation of the finely granular 
protoplasm of the primitive ovicell, or the so-called formative 
vitellus, which may easily be distinguished by its somewhat 
dark coloration from the nutritive vitellus, always com- 
mences with the cleavage of the germinal vesicle. In Argo- 
nauta the process of segmentation takes place chiefly in the 
body of the mother, and, indeed, during the movement of the 
ova in the tortuous oviducts$ ; whilst in all the other Cepha- 
lopoda observed by me the segmentation always seems to 
* In Argonauta the spawning-time lasts from May to August, in Loligo, 
Sepiola, and Ommastrephes from March to June; but I obtained mature 
ova of Sepva in Naples almost all the year round, except in August. 
+ Among the thousands of Cephalopod ova which I have examined, 
scarcely any unfecundated ova occurred. 
¢ In Argonauta to the apex of the shell, so that the female, which is 
seated in the shell, covers with her hinder parts the racemose groups of 
eggs placed within the spire. 
§ 1 observed the first stage of segmentation in ova which were taken 
out of the entrance to the oviducts, whilst in those near the orifice, eight, 
or even sixteen, segments are already present. 
