70 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



described for the same organ in Fragaroides. It consists of two sacs, 

 the first of which is an enlargement of the posterior end of the oviduct, 

 and whose cavity may be designated as the lumen of the ovary proper 

 (Plate 1 Pig. 5, lu. ov.). On the deeper wall of this sac is situated 

 the germinative epithelium, which occupies the greater part of its 

 extent. When viewed from within the animal, this epithelium 

 presents an oval outline with its long axis running in an antero-pos- 

 terior direction. The second sac, whose cavity is spoken of as the 

 lumen of the stalk tissue, is situated on the deep side of the first one, 

 and its lumen connects with that of the ovary proper by a narrow pas- 

 sage in the stalk, which is inserted in the deep wall of the ovary proper 

 at about the centre of the oval patch of germinative epithelium. 

 Figure 5 represents a cross-section through both these cavities and the 

 stalk connecting them. 



In our species the adult ovary is composed of three tissues (Plate 1, 

 Pigs. 5, 6). First the thin pavement epithelium comprising the super- 

 ficial a wall of the organ (par/). Usually it forms also the lateral 

 edges and is often continued so as to constitute part of the deep * wall 

 (Plate 1, Figs. 5, 6, 7, par."). It is directly continuous with, and of 

 the same histological structure as the wall of the oviduct, both being 

 very thin and devoid of cilia. 



Secondly, the germinative epithelium and the older ovarian follicles 

 developed from it. The former sometimes appears as directly con- 

 tinuous with the superficial wall, but more often, especially when the 

 ova are a little larger (Figs. 5, 6, 7), they seem to lie enclosed within 

 a peripheral epithelium which is itself continuous with the superficial 

 wall. The ova, which are the only indication of the germinative 

 epithelium, are very few, the total number in an adult zooid being 

 usually under twenty. Occasionally a very small oogonium, or an 

 ovum that may perhaps be considered undifferentiated (Fig. 5, ov'go.), 

 is found within the superficial Avail, but in the great majority of cases 

 they are confined to the deeper wall. Here they are usually so arranged 

 that the older the oogonium the nearer it is to the middle of the wall 

 to which the stalk tissue is attached (Fig. 5). There are very few or 

 no primordial ova in the epithelium, so that physiologically it is 

 really no germinative epithelium at all, but merely a repository for the 

 youngest oogonia. It is very interesting to note, however, that this 

 repository of oogonia takes on the same relations to the rest of the 

 ovary that the functional germinative epithelia of the more specialized 



1 Used in the technical sense defined on page 62. 



