SENSE ORGANS. 



231 



Nervous 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 a nerve 

 along each arm. The system is not separable from the 

 skin. 



Sense Organs. 



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

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



Fig. 75.- 



-Alimentary system of Starfish. 

 MtJLLER and Troschel.) 



(After 



The dorsal surface has been removed ; the digestive c^eca, the 

 stomach, &c. , are shown. 



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, 

 terminal tube foot of each ray seems to be olfactory. 



The 



