POL YZOA 



249 



red cells, 

 chambers. 



The body cavity is well developed, and is divided into 

 The sexes are united ; and the larva, known as Actino 



FIG. 128. Phoronis, much enlarged. 

 TR., Trunk; TE. t tentacles; TU.> tube. 



trocha, undergoes a remarkable metamorphosis in the course of us 

 conversion into the adult. 



Class POLYZOA or BRYOZOA 



As usually defined, the class includes two sub-classes, the Ectoprocta 

 and the Entoprocta, but it seems almost certain that these are distinct 

 classes. 



The Ectoprocta include fresh-water and marine forms, in which the 

 anus is outside the basis of the tentacles. The nervous system is repre- 

 sented by a ganglion placed between the mouth and anus. There is a 

 body cavity. There is no vascular system. Nephridia are absent, All 

 are colonial and bud very freely ; the marine forms show considerable 

 division of labour among the members of the colony. 



