XVII I 



DEVELOPMENT AND AFFINITIES 



509 



ovum in the same zooecium. According to his view, the egg is 

 fertilised by a spermatozoon after it has passed into the tentacle- 

 sheath or ovicell, or some other place where it is in free com- 

 munication with the outside water. 



Development and Affinities. Few parts of the history of 

 the Polyzoa are more fascinating than that which deals with 

 their development ; and it is probable that n other is capable 



Fig. 252. Diagrams of larvae. A, 

 Loxosoma, x 208 ; a, anus ; b, 

 brain, with left eye and ciliated 

 pit ; c, ciliated ring ; ep, epi- 

 stome ; m, mouth ; 0, oeso- 

 phagus ; st, stomach ; x, aboral 

 adhesive organ : B, Cypho- 

 nautes larva of Membranipora 

 {Electro) pilosa, x about 90 ; 

 a, vi, 0, st as in A ; c, anterior 

 part, and c', posterior part of 

 the ciliated ring ; e, epidermis ; 

 ms, adductor muscle of shells ; 

 p, pyriform organ, of unknown 

 function ; sh, shell ; v, vesti- 

 bule ; the " internal sac " or 

 sucker, by which fixation is 

 effected, is seen between a and 

 ms. (B, after Prouho.) 



of giving so much insight into the affinities of the several groups 

 to one another and to other groups of the animal kingdom. 



The comparative study of the larvae of the Polyzoa may be 

 said to date from 1877, when J. Barrois published an elaborate 

 Monograph x on this subject. Although some of Barrois' earlier 

 opinions have been subsequently modified, this work still gives 

 the best figures of the external form of the beautiful larvae of 

 many genera. A detailed account of the larval forms of Polyzoa 

 must be omitted from want of space ; and the general conclusions 

 only can be given. 



1 Recherches sur VEmbryologie cles Bryozoaires, 4to Lille, 1877. 



