562 POLYZOA. 



budding from the primary zooecium, or as a process of meta- 

 morphosis in which the larval organs undergo degeneration and 

 new formation in consequence of the extensive changes compressed 

 into the metamorphosis. Until this point is settled it is impossible 

 to relate with certainty the adult organs and surfaces to those of 

 the larva, because of the extensive degenerative changes and new 

 formations which take place at the metamorphosis. 



If the formation of the first polypide is a case of budding, 

 we ought, in determining the* homologous surfaces of the primary 

 zooecium and first polypide, to attach no more importance to the 

 fact that apparently the oro-anal surface of the first polypide is 

 derived from the aboral surface of the larva, because it is formed 

 from it, than we should to the fact that in a bud developed from the 

 dorsal surface of the adult, the oro-anal surface of the budded form is 

 derived from the dorsal (aboral) surface of the parent. Consequently 

 the argument of Korschelt and Heider, which is based upon this 

 consideration, and from which they deduce most far-reaching con- 

 sequences, that the oro-anal line of CypTionautes and other Ectoproct 

 larvae is really dorsal has no value. Moreover, on the same 

 hypothesis, the fact that in the formation of the first polypide the 

 ectoderm of the primary zooecium apparently gives rise to the 

 alimentary canal has 110 more importance than a similar phenomenon 

 would have in ordinary gemmation, in which the value of the layers 

 is not the same as in embryonic development. 



It must be noted here that in the embryonic origin (not described in this work) 

 of the larvae of the Ectoprocta without alimentary canal, the endoderm is, in 

 some cases, not formed at all ; the internal tissue being, to judge by its fate, 

 entirely mesodermal, and any cavity in it entirely coelomic (vide especially the 

 larva of Phylactolaemata). The endoderm appears only in the first bud, and is 

 in that derived from ectoderm. 



Finally, to sum up the matter, if the larva is a trochosphere and 

 the ciliated disc an apical plate, and if we regard the formation of 

 the first polypide as a case of budding from the primary zooecium, 

 which is the metamorphosed larva ; and if moreover there is in the 

 Polyzoa, as there is in other animals, an homology between the 

 mouth and anus and ventral surface of an organism produced by 

 budding and the corresponding structures in the parent organism; 

 then it follows that the oro-anal line of the Ectoprocta is ventral, and 

 the ganglion a suboesophageal ganglion, and to be compared to the 

 suboesophageal ganglion of other types : that is to say, it is not 

 dorsal as might be surmised from the terminology applied to the 



