POLYZOA 



531 



A remarkable phenomenon very characteristic of the Polyzoa is the 

 formation of the brown body. Tentacles, gut, in fact the whole of the 

 polypide, degenerates and forms a brown, compact mass. A new poly- 

 pide is regenerated from the zooecium and the brown body often 

 comes to lie in the new stomach and is evacuated through the anus. 



m.retr. 



Stat 



Fig. 391. View of right half of P/z/wa^eZ/a/ww^o^a, slightly diagrammatic. After 

 Allman and Nitsche. an. anus; bzo. body wall; ep. epistome;/n. funiculus; 

 ga. ganglion; int. intestine; Iph. lophophore; M. mouth; m.retr. retractor 

 muscles of polypide; oe. oesophagus ; ov. ovary; sp. spermatozoa; st. stomach; 

 Stat, statoblast; t. testis; t.' the same, more mature; tb. wall of tube; ten. 

 tentacles. 



This periodical renewal of the individual is a normal process in most 

 polyzoa. It was formerly explained as due to the accumulation of 

 excreta in the absence of specific excretory organs. It can, however, 

 be hardly doubted that animals so small and with so great an area of 



34-2 



