458 TUNICATA. 



C. Pallial Gemmation of the Botryllidae. 



In the Botryllidae also, the buds early show a certain inde- 

 pendence, the entodenii-vesicle * found in each of them becoming 

 separated from the parent-animal, and the connection between them 

 and the parent-animal consisting Utter merely of a hollow, stalk-like 

 ectodermal process. In this case, the buds are not produced from 

 a stolon arising at the above-mentioned point, but as simple out- 

 growths of the body-wall at the sides of the branchial sac. Della 

 Valle on this point agrees with the older authors (Metschnikoff, 

 Ganin, Krohn, Giard, and others), and this view has been quite 

 recently confirmed by Hjort (No. 59) and Oka (No. 64a). This is 

 the type of budding described by Giard (No. 57) as " bourgeon ne- 

 ment palleal ". There is usually only one bud on one side of the 

 body about on the level of a line cutting oft' the upper third of the 

 branchial sac. Occasionally, however, two buds are found, one to 

 the right and the other to the left. 



The first rudiment of the bud consists of a bilaminate outgrowth 

 of the body-wall (Della Valle, H.tort and Oka, who confirm 

 Metschnikoff's statements on this point). The outer layer is 

 formed by the ectoderm, the inner layer, on the contrary, which 

 yields the entoderm- vesicle of the bud, is said to originate as an 

 outgrowth of the wall of the peribranchial sac in the parent. 



It was formerly thought (by M. Sars, Kolliker, and others), that, in the 

 Botryllus larva, budding commence during the free-swimming stage, and 

 that eight processes, which surround the anterior end of the larva in a circle, 

 represent the rudiments of a similar number of buds. In this way, the first 

 cycle of individuals were said to arise surrounding a common cloaca. The 

 later researches of Metschnikoff (No. 41), Krohn (Nos. 62 and 63), and Ganin 

 (No. 55), have shown that so-called mantle-vessels have in this case errone- 

 ously been regarded as buds. Budding begins only after attachment, a single 

 bud forming first. While this bud grows, the primary individual of the colony 

 disintegrates. The daughter-individual then produces two buds, one on the 

 right and the other on the left side of its body. These two individuals of the 

 third generation continue to grow, while the individual that produced them 

 dies. By a repetition of the process in the third generation, a colony con- 

 sisting of four individuals (of the fourth generation) arises. The four 



* [According to Hjort (No. XIV.) and Pizon (No. XXVI.), the inner vesicle is 

 not derived from the entoderm of the parent, but from the peribranchial 

 cavity which arises in the larva as a pair of ectodermal invaginations. Conse- 

 quently these observers conclude that all the orgaus of the bud in Botryllus 

 are formed from the ectoderm. This condition, if true, is very remarkable, as 

 it differs in toto from what is known of the development of the inner organs in 

 the buds of other Ascidians. — Ed. J 



