M. Ussow’s Zoologico-Embryological Investigations. 101 
deletii, Leach, and Loligo sagittata, Lam.) and one Octopod 
(Argonauta Argo, Linn.). 
For the more convenient exposition of the facts discovered 
by me, I shall divide this communication into two halves. 1. 
Anatomico-physiological data relating to the structure of the 
female generative organs and the mode of formation of the ova*. 
2. The results of my embryological investigations upon :— 
a, the process of segmentation ; 6, the formation of the blasto- 
derm and the production of the germ-lamell (first period ot 
development) ; and ¢, the original foundation of the organs up 
to the appearance of the typical Cephalopodal form (second 
period of development). As the development of the above- 
mentioned Cephalopoda is very concordant in essential points, 
I shall not describe the development of the individual species, 
but the course of development in all the four species, in order 
to be as concise as possible. 
I. The structure of the ovaries and the mode of formation of 
the ova of the Cephalopoda. 
In youngish female individuals of various species of Cepha- 
lopoda, the unpaired, rather large ovary, enclosed in the peri- 
toneal sac, and situated in the lower, narrower part of the 
mantle, consists of numerous cecal, ramifying tubules, which 
form its glandular parenchyma. In general the structure of 
the ovary is like that of the ovary in the Vertebrata, especially 
in Birds and Tortoisest. There may be distinguished in it :— 
a, the very thin sheath (theca follicul’), consisting of fibrous 
connective tissue; , the internal, one-/ayered epithelial mem- 
brane (membrana granulosa), which lines the inner surfaces 
of the above-mentioned tubular and vesicular ovarian spaces 
quite uniformly. In the first of the above-mentioned coats 
ramifies the thin artery (genital artery), which takes its origin 
from the lower part of the ventricle. The Graafian follicles 
are formed at different periods of the spawning (as may be 
* Besides the above-mentioned species, I have investigated the mode 
of formation of the ova and some stages of development in Ommastrephes 
todarus, Rossia macrosoma, and Sepia bisertalis, Montf. 
+ I am at present occupied with the study of the last period of deve- 
lopment of the Cephalopoda, namely the development of the embryo, 
which I am enabled to do by means of a great store of remarkably well- 
preserved material. The production of the organs is of especial im- 
portance in comparative embryology; and to this [ have particularly 
directed my attention. 
{ As made known by Gegenbaur’s investigations (Arch. fiir Anat. &c. 
1861, p. 491); Hiss, Erste Anlage der Wirbelth. p. 19 e¢ seg. pl. ii.; and 
Waldeier, Der Eierstock, pp. 48 & 69, pl. iv. 
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