558 



POLYZOA. 



FIG. 447. A, larva of Alcyonidiitm mytili(a.fter Barrois). B, diagram 

 of longitudinal section through the larva of Alcyonidiiim (after 

 Harnier), both from Korschelt and Heider. c cells of the velum ; 

 <7 ganglion (? cerebral) in connection with the ciliated disc and 

 pyriform organ o; 711 mouth; p mantle-groove; r ciliated disc; 

 s adhesive organ (sucker). In these figures the oral surface is 

 directed downwards, whereas in Figs. 445 and 446 it is upwards. 



which the rec- 

 tum (r) opens. 

 The alimentary 

 canal consists of 

 the pharynx (pli), 

 oesophagus, sto- 

 mach (es) and 

 rectum (r). Just 

 in front of the 

 anus on the floor 

 of the vestibule 

 there is an in- 

 vagination of 

 thickened ecto- 

 derm ; this is the 

 adhesive organ 

 (ad), by which 

 the larva attach- 

 es itself. There 

 are two shell- 

 plates placed 

 right and left 

 on the aboral 

 surface. They 



Fio. 448.^, larva of Biigula plumosa (after Barrois). B, diagram of median section through 

 a larva of Bugula (after Vigelius), both from Korschelt and Heider. c cells of velum ; 

 c groove of pyriform organ ; / internal tissue of the larva ; o pyriform organ ; p mantle- 

 groove ; r ciliated disc ; s adhesive organ or sucker. 



