THE STELLEROIDEA 



245 



ring, from which a branch runs up each ray between the rows of 

 tube-feet, and external to the pseudhaemal radial vessel. Each 

 branch gives off nerves to the tube-feet and ectoderm of its ray. 

 The second set of nerves consists of bands lying internal to the 

 radial branches of the first set ; they lie along the perihaemal canal, 

 which surrounds the pseudhaemal vessel ; the branches from these 

 nerves supply the muscles of the ambulacral ossicles. The third 

 group of nerves is abactinal in position ; there is a ring round 

 the anus, giving off a branch along the upper side of each ray, and 

 innervating the muscles of the body wall. 



The Genital Organs of Asterias consist of ten branched glands, 



Culcita grex. 



a pair being situated on the dorsal side of each ray close to the 

 disc. Each gland has a separate aperture on the abactinal surface. 



The only special respiratory organs are a series of long, tubular 

 prolongations of the body -cavity, known as papulae, dermal 

 branchiae, lymph gills, or branchial vesicles. In Asterias they 

 occur on all sides of the rays and disc. 



The most interesting sensory organ of Asterias is a small 

 eye-spot on the terminal podion of each ray (Fig. XXV. on 

 p. 30). The animal has an olfactory sense, for it will follow 

 food, even after the eye-spots have been destroyed ; the situation 

 of this sense is diffuse, for any part of a starfish arm that can 

 move independently will follow food (Romanes) ; but Prouho 

 limits the sense of smell to a few podia near the end of the ray, 

 which he calls " palps." 



