100 INTRODUCTION TO ZOOLOGY CHAP. 



organs in the body seem to disintegrate, forming a conspicuous 

 " brown body " inside the zooecium, after which process, from 

 the still active body-wall, new organs are formed, so that the 

 " brown body " may come to lie within the stomach of the 

 rejuvenated individual, and finally it may pass out of the anus. 

 This " brown body " is a conspicuous object, which is sure to 

 be observed by any student of Polyzoa. 

 Eeproduc- The individual zooids are hermaphrodite in 

 tion. most Polyzoa. 



The reproductive organs are formed either from the body- 

 wall, or from a cord of tissue called the funicle (Fig. 52, fume), 

 which stretches from the stomach to the body-wall. The 

 eggs often develop for some time within a special pouch of 

 the zooecium (Fig. 52, emb). 



In some fresh-water colonial forms, such as 

 * ne f ree - mov i n g Cristatella, which dies in the winter, 

 special structures known as statoblasts are formed ; 

 these persist after the death of the individual zooids, and 

 give rise to new colonies in the spring. 

 Such statoblasts consist of small buds, 

 formed from the funicle ; they become 

 enclosed in two horny concave shells, 

 wn i cn are kept tightly closed and serve 

 as an efficient protection in the winter. 

 FIG. 54. Statoblasts of These fresh-water forms are further 

 Polyzoa. (From the Cam- characterised by the tentacles being 



bridge Natural History.) 1-11 



arranged in a horse-shoe curve, instead 

 f i" row, as in the marine Polyzoa 

 The oval colony of Cristatella may 

 be over two inches long (Fig. 55). It creeps along on its 

 flat under surface, whilst the zooids project from the upper 

 convex surface of the greenish jelly-like mass. It is found in 

 shallow still water, creeping over the stones or weeds in sunny 

 spots. The statoblast of Cristatella is peculiar because of the 

 hooked spines which surround it (Fig. 54). 



Lophopus is another, but smaller, fresh-water colony, which 

 may be found on duckweed, looking like a little speck of jelly 

 until it expands its beautiful horse-shoe of tentacles (Fig. 56). 

 It also can move, though but slowly, over the surface on which 

 it lives. The statoblasts are shown in Fig. 54. 



Plumatella forms branching, thread-like colonies, adherent, 



