I 



XVIII 



LARVAE 



511 



Entoprocta, and ending with the Phylactolaemata. Alcyoni- 

 dium (Fig. 253, B) possesses a rudimentary alimentary canal, 1 

 although the most conspicuous structures are those connected 

 with the fixation and other phenomena of larval life. The 

 larvae of many of the encrusting Cheilostomes (Fig. 253, A) 

 resemble that of Alcyonidium, while those of Bugula, Scrupocel- 

 iaria, etc., belong to a type easily derivable from that of the 

 encrusting forms. The branching Ctenostomes (Boiverbankia, 



Fio. 253. A, Aboral view 

 of free larva of Lepralia 

 foliacea Ell. and Sol. ; 

 a, long cilia of pyriform 

 organ ; g, aboral groove : 

 B, longitudinal section 

 of embryo of Alcyoni- 

 dium, x 135 ; c, ciliated 

 ring ; g, aboral groove ; 

 m, mouth ; n, nervous 

 system ; p, ' pyriform 

 organ," of unknown 

 function ; s, " internal 

 sac " or " sucker," by 

 which fixation is ef- 

 fected : st, stomach. 



etc.) have a larva which may be regarded as derived, along 

 slightly different lines, from that of Alcyonidium. The Cyclo- 

 stomata and the Phylactolaemata have the most modified forms 

 of larva. That of the former group may owe some of its 

 peculiarities to the occurrence of a remarkable process of embry- 

 onic fission, which takes place in the ovicell, and as the result of 

 which each egg gives rise to a large number of larvae." The 

 Phylactolaemata have a larva which is not unlike that of 

 Bowcroankia. 



We have seen that the larva at fixation becomes a zooecinm, 



1 Arch. Zool. Exp. 2 ser. v. 1887, p. 446. 

 Quart. J. Micr. Sci. xxxiv. 1893, p. 199 ; xxxix. part i. 1896, p. 71. 



