POLYZOA. 249 
red cells. The body cavity is well developed, and is divided into 
chambers. The sexes are united;.and the larva, known as Actino 
h VAN 
an 
), 
, 
yy 
Fic. 128.—Phoronis, much enlarged. 
TR., Trunk; TZ., tentacles; 7U., tube. 
trocha, undergoes a remarkable metamorphosis in the course of its 
conversion into the adult. 
Class PoLyzoa or BRyYOzoA 
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 isa 
body cavity. There is no vascular system. Nephridiaareabsent. All 
are colonial and ‘bud very freely; the marine forms show considerable 
division of labour among the members of the colony. 
