36 IX VERTEBRATE ANIMALS. 



tozoa than to any other. In these forms (fig. 16) the body is pro- 

 vided with long filamentous pseudopodia, which stand out like rays, 

 and which may anastomose with one another. The body may be 

 quite soft, as in the common "Sun-aniraalcule" (^e<i/iO/j/(ry«), but 



Fig. 16. — Heteropknis spfni/era, one of the Heliozoa, greatly enlarged 

 (after Heitwig and Lesaer). c c Contractile vesicles. 



there may be, and often are, delicate spines of flint radiating from 

 the central sarcodic mass, and there is sometimes a regular siliceous 

 skeleton. The Helioztia are fitrther furnislied with the structures 

 which are known as the " contractile vesicle " and " nucleus.'' 



