446 THE ANIMAL KINGDOM. 



organism remains attached by processes of the test. The tail atrophies, 

 and some of its cells appear to become blood-corpuscles, whilst the shape 

 of the body undergoes profound changes. Except in the Larvacea, in the 

 sexual forms of Thaliacea^ and the majority of A. Simplices, asexual 

 generation takes place by budding or fission. In the Clavellinidae there is 

 a creeping stolon which produces buds, and the new organisms remain in 

 vascular connection with the parent. In the A. Compositae and A. Salpae- 

 formes colonies are formed in which the individuals are enveloped in a 

 common test. As to the Compositae the larva buds in Distaplia and 

 continues to develope, whereas in Pseudodidemnium gelatinosum it dies 

 away, and in Amareucium proliferum the post-abdomen (i.e. hind section of 

 the body) divides transversely into several pieces, each of which becomes a 

 new zooid, whilst the parent grows a new post-abdomen. In Botrylhis the 

 first individual is asexual, buds, dies away, and this process is continued for 

 several generations. The zooids thus formed are arranged in star-like 

 groups (systems or coenobii) round a common cavity, into which their 

 atrial pores open. The germinal disc in Pyrosoma developes in the pos- 

 terior region into a transitory Cyathozooid, in the anterior into the four 

 first Ascidiozooids of the colony, which are connected to or continuous 

 with the Cyathozooid. Alternation of generations occurs in the Thaliacea. 

 The asexual generation or nurse has a ventral posterior stolon. This 

 stolon grows to a great length in Salpa, and is constricted into a series of 

 buds, which remain connected for a lengthened period, and are set free 

 collectively from the parent as sexual or chain Salpae. The chain is 

 eventually broken up. In Doliolum the stolon is small. It developes a 

 number of primitive buds, which are set free, and creep over the parent by 

 means of pseudopodial processes of the ectoderm cells. They become 

 attached to a dorsal and posterior process of the body, where they multiply 

 by transverse division, and are arranged in linear series, two lateral and 

 one median. The dorsal process lengthens as the number of buds increases. 

 The lateral series of buds grow into nutritive zooids. The epithelium of 

 the stolon, and of the bases of these zooids, is peculiarly modified, and the 

 products of digestion appear to pass from the zooids to the parent, which 

 loses its pharynx and digestive tract whilst its muscle-bands enlarge. The 

 zooids of the middle series grow, and are eventually set free as foster- 

 mothers. The foster-mother is asexual, and carries away attached to its 

 peduncle a few primitive buds, which divide, forming fourteen to twenty 

 secondary buds. These develope into the sexual Doliolum. The ovum in 

 both Salpa and Doliolum produces the nurse. Anchinia probably resembles 

 Doliolum more or less closely. The cylindrical body with attached buds, 

 which become sexual animals or produce creeping buds, is probably a 

 detached part of a dorsal (?) process. The nurse is not known unless it is 

 the form from Naples described by Wagner. 



