BANCROFT: OVOGENESIS IN DISTAPLIA OCCIDENTALIS. 69 



formed by a cylindrical epithelium in both Clavelina rissoana and 

 Fraf^aroides, and to which the stalks of the older follicles are attached, 

 is considered as having developed from the germinative epithelium. 

 According- to this view, then, both the germinative epithelium and the 

 cylindrical epithelium connecting with and forming the stalks of the 

 follicles ^ are merely differentiations from the wall of the ovary and not 

 additional structures. In other words, the ovary is but a specialized 

 part of the oviduct. 



On the other hand, Julin (p. 95) finds that in Styelopsis the super- 

 ficial wall of the ovary connects with a thin limiting epithelium and 

 not with the germinative epithelium. The latter represents an addi- 

 tional element lying within the cavity formed by the two peripheral 

 epithelia and not represented at all in the oviduct of such forms as 

 Clavelina and Fragaroides. As the ova increase in size, they push the 

 limiting epithelium before them, and retain their connection with the 

 rest of the ovary by means of it. Thus, according to this author, the 

 outermost layer of cells surrounding the ovum and continuous with 

 the stalk is not, as has been formerly supposed, derived from the 

 germinative epithelium, and is not part of the true follicular covering 

 of the egg. 



Floderus, though he finds a limiting epithelium in the young 

 ascidian, does not agree with Julin concerning the structure of the 

 adult. He finds that the germinative epithelium continues into the 

 epithelium of the superficial wall (p. 187), that the epithelium which 

 he thinks corresponds to Julin's limiting epithelium does not connect 

 with the superficial wall (p. 185) , and that the stalks of the ova con- 

 nect with their follicles (p. 190). 



But little evidence in favor of Julin's contention has been found in 

 the ovary of Distaplia occidentalis, which has essentially the structure 



(p. 351) as "la voute de cette raeme cavite" is the deep or ventral wall. Maurice 

 (p. 459) takes it for granted that this wall is dorsal, and points out the difference 

 that would exist between Clavelina and Fragaroides on this point. Floderus 

 (p. 183-184) discusses the question fully and concludes that although van Beneden 

 et Julin do not state explicitly which side is dorsal, the description and the posi- 

 tion of the figure when compared with the other figures on the plate compel us to 

 believe that the authors consider the " voute " dorsal. However, leaving the ques- 

 tion of the intention of the authors aside, the ventral position of the germinative 

 epithelium in the fundament of the ovary in C. rissoana and of the ovarian follicles 

 in the adult ovary of C. lepadiformis, described by Floderus, point conclusively to 

 the fact that the same condition must obtain in the adult C. rissoana. 



1 I propose in future to call the characteristic tissue constituting this epithelium 

 stalk tissue. 



