68 bulletin: museum of comparative zoology. 



2. Structure in the Adult. 



a. In Distaplia occidentalis. 



This species of Distaplia is always hermaphroditic, no unisexual 

 zooids such as have been described for D. magnilarva having been 

 encountered. Nor is there any provision for the prevention of self- 

 fertilization by means of protandry or protogyny. The testis is found 

 to be functionally active for a much longer period than the ovary, for 

 spermatozoa are always found in the vas deferens from the time the 

 oldest ova are about half grown until after the usual number of eggs, 

 two, has been laid. 



The development of the genital organs in zooids of the same size 

 varies considerably according to the condition of the colony. If the 

 oldest zooids of a colony are laying eggs or have recently done so, then 

 all the younger ones and the older buds have their sexual organs more 

 fully developed than in individuals of the same size in colonies which 

 possess no mature sexual products. In the undifferentiated buds, 

 however, the same conditions obtained in all the colonies. 



The position of these organs is on the right side of the intestinal 

 loop. When partially developed, they do not extend beyond the 

 intestine, either anteriorly or posteriorly, but when maturity is reached, 

 they project beyond it in both directions. In this condition the ovary 

 occupies the extreme hind end of the zooid and is entirely posterior 

 to the loop. The testis, which is much more voluminous, is also 

 mainly posterior to the loop, but its extreme anterior end is usually 

 within it. 



Concerning the finer structure of the ovary, recent investigators are 

 not entirely in accord. Corresponding to the fact that in the develop- 

 ment of this organ a peripheral epithelium is described by Julin and 

 Floderus, which the earlier investigators had not mentioned, there is a 

 similar disagreement about the adult structure. But here the differ- 

 ence is of much more importance, for Julin, in tracing the peripheral 

 membrane into the adult ovary, arrives at an idea of the relation of 

 the germinative epithelium to the peripheral wall essentially different 

 from that of his predecessors. Van Beneden et Julin ('85, pp. 350, 

 358) and Maurice ('88, p. 456, 464) had found that the superficial 

 wall of the ovary passed insensibly into the germinative epithelium 

 occupying the lateral edges of the organ. The deeper 1 wall, which is 



1 There can be no doubt that in van Beneden et Julin's Figure 14 (Planche XV.) 

 the wall of the ovary of Clavelina rissoana that is placed uppermost and described 



