AESTIVATION OF BOTRYLLOIDES GASCOI DELLA VALLE. 151 



ding zone in Botryllus) might not remain undifferentiated and retain the power of 

 entering into the development just as does the ectoderm of the larva. In the case 

 of this sestivating colony, however, no such objection could be made, for buds may 

 happen to lodge anywhere in the vascular system and development ensue. Thus, 

 if any part of the ectoderm is to remain undifferentiated so as later to develop buds, 

 the whole of the ectoderm of the blood-vessels would have to do so. 



III. DEVELOPMENT OF THE BUDS. 



The details of the development of these buds have not been followed, as the 

 material was scanty and the conditions rather unfavorable on account of the masses 

 of degenerating cells that filled the blood-vessels. But enough was seen to make it 

 probable that the process is about what has been described in the cases of Botryllus 

 and Goodsiria. However, a few minor differences have been noted. Thus, a part 

 of the wall of the undifferentiated inner vesicle is several cells thick, while the rest is 

 very thin (Figs. 11, 12). The developmental processes beginning with the folds 

 producing the peribranchial sacs start when the bud has reached a greater size than 

 in the case of buds which are still attached to their parent zooids. 



IV. ORIGIN OF THE ISOLATED BUDS. 



As has already been said, no evidence for the development of zooids from ampullae 

 was observed. The buds wherever seen were perfectly well defined, and never pre- 

 sented the appearance of being formed by an aggregation of blood-cells, although in 

 some cases the cavity of the inner vesicle was almost entirely closed. 



Herdman ('86, pp. 59, 90) describes the origin of buds from aggregations of blood- 

 cells for Sarcobotrylloides wyvillii and Colella pedunculata. It appears, then, that 

 in these species there are buds in vessels just as in Botrylloides gascoi. But in all 

 three cases the buds may have been produced elsewhere and have migrated into the 

 vessels. 



As no evidence in favor of an intravascular nor intra-ampullar origin of the 

 isolated buds was detected, I feel convinced that they were developed from the 

 zooids of the original colony before these had degenerated entirely. The buds 

 must have severed their connections with the parent zooids, and must have been 

 carried into the yellow lobe that was then being formed. There they remained dor- 

 mant for a while, nourished by the circulation maintained by the ampullae, until 



