No. 19.] 



ECHINODERMS OF CONNECTICUT. 



23 



Both ampullae and tube-feet have highly muscular walls, and 

 both are filled with fluid from the water-vascular system. When, 

 in locomotion, the ampulla of any particular tube-foot is con- 

 tracted, the fluid contained therein is forced into the tube-foot 

 itself, extending this organ until it becomes a long, finger-like 

 process. On coming in contact with any external object the 

 disk at the end of the tube-foot may be pressed tightly against 

 it. If now the muscles of the tube-foot contract, the water which 



Fig. 1. Transverse section of a decalcified ray of a young starfish, 

 showing the relations of the internal organs. The two ampullae (amp) 

 open by wide canals into the tube-feet (t), the water supply of which is 

 provided by the radial canal (re). The openings into the ampullae from 

 the radial canal are furnished with delicate valves, as indicated, which pre- 

 vent the back flow of the water when the ampullae are contracted and the 

 tube-feet extended. Beneath the radial canal are the two radial perihaemal 

 vessels (rv), separated by a vertical septum, and beneath these is the 

 radial nerve-cord (n), which extends from the circum-oral nerve to the 

 tip of the ray. Sections of the spines (s), branchiae (b), and pedicellariae 

 (p) are indicated. The pyloric caeca (h) are attached by mesenteries to 

 the dorsal wall of the ray. The spaces between the organs constitute the 

 ccelom (c), and are in life rilled with a fluid somewhat resembling the 

 blood, and like it containing floating corpuscles. 



