250 



ECTOPROCTA. 



the larvae hitherto described. The researches of Barrois (No. 298) and 

 Metschnikoff (No. 314), (but especially those of the former ou the early 

 stages of Fiustrella hispida, the larva of which is very similar in form 

 to Cyphonautes, though without so great a complexity of organisation), 

 have given a satisfactory basis for a general comparison of Cypho- 

 nautes with other ectoproctous larvae. 



The segmentation and early stages of the embryo of Fiustrella 

 resemble closely those of Alcyonidium. A projecting ring of large 

 cells is formed, dividing the larva into oral and aboral parts. The 

 oral part soon however becomes very small as compared with the 

 aboral, and becomes vertically flattened so as to be nearly on a 

 level with the ring of large cells. In the next stage the flattening 

 becomes completed; and the ring of large cells 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 LAKVA OF FLUSTRELLA HISPIDA. (After BarroifO 

 wi(/) groove above dorsal organ ; Ph. dorsal organ; st. stornodfeum (?) ; 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 com- 

 pressed. 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 



