Budding in Peroplioia. 139 



more to assume a symmetrical position. The two longitudinal 

 folds, which grow rapidly and run in obliquely to meet each 

 other, do not come together on the dorsal surface of the 

 vesicle, but some distance below it. The result of tliis is 

 that, when the right and left peribranchial sacs are separated 

 from the inner vesicle, a median dorsal portion connecting the 

 lateral sacs is cut off at the same time. This median piece, 

 the cloaca, therefore does not arise from the fusion of the 

 lateral sacs dorsally, but the three parts are constricted off 

 together. This is essentially the same process as that which 

 Pizon * and Hjort (/. c.) have described for Botryllus. 



In Perojjhora viridis the folds which separate the peri- 

 branchial cavity from the inner vesicle do not involve the 

 entire length of the latter, but leave nearly the whole of 

 the anterior half undivided, as well as a short portion at the 

 posterior end. 



When the right and left sacs are being formed, as just 

 described, a broad pouch or diverticulum grows out from the 

 anterior margin of each and gradually spreads over the 

 undivided portion of the inner vesicle. These pouches are 

 merely continuations or extensions of the lateral sacs, and 

 later completely cover the sides of the anterior region of the 

 branchial sac. 



Similar prolongations are carried out from the posterior 

 margin of the sacs, and, though not prominent at first, as the 

 bud becomes older and increases in length they attain a con- 

 siderable size. 



According to Pizon {I. c.) in Botryllus the inner vesicle 

 gives off two posterior lateral diverticula, which are cut off 

 together with the peribranchial cavity, and then appear as 

 posterior prolongations of the latter, with which they always 

 remain in communication. They are what Pizon calls the 

 '''■ diverticules perivisceraux,'''' and from the fact that they arise 

 as diverticula from the posterior end of the inner vesicle, he 

 regards them as homologous with the epicardial sacs of some 

 other Ascidians. If this relationship is true, the connexion 

 of the " epicardial sacs " in Botryllus with the peribranchial 

 cavity is probably the result of the early separation of the 

 latter from the inner vesicle. 



In the light of these considerations it is possible, then, that 

 the posterior extensions of the peribranchial sacs in Peropliora 

 viridis have the same significance ; but it is to be borne in 

 mind, however, that if such be the case, their direct origin 

 from the inner vesicle has been lost completely, as they do 



* Ann. Sc. Nat., Zool. (7) t. xiv., 1S93. 



10* 



