302 



ECTOPROCTA. 



surrounds, like the vestibule of the Entoprocta, a flat oral disc. 

 The aboral side is dome-shaped, and forms the greater part 

 of the embryo. 



FIG. 132. ADVANCED LARVA OF FLUSTRELLA HISPIDA. (After Barrois.) 

 in (?) groove above dorsal organ ; Ph. dorsal organ ; st. stomodreum (?) ; s. ciliated 

 disc at aboral end of body. 



In the next stage a small disc the ciliated disc is formed 

 in the middle of the aboral dome. The larva becomes laterally 

 compressed. The ring of large cells which now constitute the 

 edge of the vestibule is covered, as in the larva of Pedicellina, by 

 cilia, which are specially long in front of the dorsal organ. 



In the next stage the ciliated disc (fig. 132, s.) becomes 

 reduced in size, but surmounted by a ring of cilia round the 

 edge, and a tuft of cilia in the centre. The chief difference 

 between this larva and that of Alcyonidium depends on the 

 small size of the ciliated disc, and the oral position of the ciliated 

 ring in the former. There are intermediate types between these 

 forms of larvae. 



This stage immediately precedes the liberation of the larva. 

 The free larva differs from that in the ovicell mainly in the 

 possession of a shell formed as a cuticular structure, composed 

 of two valves placed on the two sides of the embryo. The 

 aboral ciliated disc, still more reduced in size, loses its cilia, and 

 becomes enclosed between the two valves of the shell. 



The post-embryonic metamorphosis follows, so far as is known, 

 the course already described for the larva of Alcyonidium. 



