Wi'] Ritier-Forsyih: Ascidians of Southern- California 4:67 



fall inertly to the bottom, though an occasional one escapes from the 

 egg membrane and s\vim.s with a wriggling motion immediately on 

 emerging from the parent. Although the larvae have a free swim- 

 ming period, this is very short. It lasts but a few hours at the most, 

 nor is the swimming executed during the period sufficiently vigorous 

 and determinative to make it count for much if anything in the dis- 

 tribution of the species. In view of the very brief swimming period 

 in the larval life of this and of several other species of Ascidians, the 

 general question of the significance of larvae in the group becomes of 

 interest and suggests a systematic study of the point. 



Bancroft (1899) describes some interesting features of the repro- 

 ductive system of Distaplia occidentalis, from which we quote: 



The most striking peculiarity of the oviduct is that its diameter, even when 

 distended by the passage of the ovum, is very much less than the normal 

 diameter of the ripe egg. Accordingly, when the egg is passing through the 

 duct, it is greatly distorted, assuming the shape of a sausage. 



With regard to the incubatory pouch he says : 



A careful examination of the structure of the pouch shows that it is not 

 merely a diverticulum from the peribranchial sac, but consists of two parts 

 which, for descriptive purposes, may be called the oviduct and the peri- 

 branchial portions, though I do not know that they have been developed from 

 the oviduct and peribranchial sac respectively. The oviducal part is a narrow 

 tube, the anterior end of which connects with the oviduct, and the posterior 

 end with the bottom of the pouch. Anteriorly the peribranchial portion is a 

 narrow tube opening into the posterior dorsal corner of the right peribranchial 

 sac. Posteriorly, it is enlarged to form the pouch proper, in which the develop- 

 ing embryos are lodged. The oviducal portion of the pouch is a continuation 

 of the oviduct into the pouch, and the egg never reaches the peribranchial sac 

 at all, but is conve3'ed directly to the bottom of the pouch. ... As the pouch 

 is completely separated from its zooid long before the larvae are mature, the 

 only function of this peribranchial orifice is to serve as a passage of the 

 spermatozoa. 



Our observations, as reference to plate -15, figure 6-4 will show, 

 confirm Bancroft's account of the incubatory pouch, but leave the 

 que-stion as to the exact method by which the eggs get into it un- 

 an.swered. 



The two species of the old genus Distoma treated in this paper 

 belong to Caiillery's subgenus Eudistoma. 



Eudistoma psammion, n. sp. 



ri. 44, figs. 52 and 53 



Superficial characteristics of the colony. — Massive, though encrust- 

 ing ; hard, largely because of much sand in deeper layers of test ; 

 thickness in thickest part about 2 cm. ; not thin in any part ; expanse 



