STAR- FISH. 



243 



wall. Other muscles affect the size of the ventral grooves, 

 and muscular elements also occur on the protrusible part 

 of the stomach, and in connection with the water vascular 

 system. 



Underneath the ciliated ectoderm lies a network of nerve 

 fibrils, with some ganglionic cells. But besides these 

 diffuse elements there is a pentagon around the mouth, and 





115. Star-fish. 



I. Ventral surface; t.f., tube-feet extended; a.g:, the ambulacral 

 groove with the tube-feet retracted ; ;., the mouth. II. Dorsal 

 surface, showing the position of the madrepore (-I/.); the two 

 adjacent arms form the bivium. 



a nerve along each arm. The system is not separable from 

 the skin. 



A red eye spot, sensitive to light, lies on the terminal 

 ossicle at the tip of each arm, and is usually upturned. It 

 is a modified tentacle, bearing numerous little cups, lined 

 by sensitive and pigmented cells, containing clear fluid, and 

 covered by cuticle. The skin is diffusely sensitive. The 

 terminal tube-feet of each ray seems to be olfactory. 



The star-fish may be found with part of its stomach 



