SECT. vi. ECHINODERXATA. 171 



motive and prehensile. From these a canal extends 

 through the centre of each ray, which in its course 

 sends off lateral branches to the bases of the feet to 

 supply them with liquid. The whole of this system of 

 vessels and feet are lined with vibratile cilia, which 

 maintain a perpetual circulation in the liquid. 



The toothless mouth on the under-side of the disk 

 dilates so as to admit large mollusca with their shells. 

 The short gullet and stomach are everted, protruded 

 through the mouth, and applied round the object to be 

 swallowed, which is then drawn in, digested, and the 

 shell is discharged by the mouth. However, in three 

 orders of this family there is a short intestine and 

 vent. From the large stomach, which occupies the cen- 

 tral part of the disk of the star-fish, a couple of tubes 

 extend to the extremity of each ray, where they secrete 

 a substance essential for digestion : the stomach is in 

 fact a radiating organ, partaking the form of the animal 

 it sustains. 



A pulsatory vessel near the gullet propels the yellow 

 blood into a system of fine tubes, that are spread over 

 the walls of the stomach and its rays. Through these 

 walls the blood receives a nutritious liquid, which it 

 carries with it into a network of capillary vessels, 

 widely extended throughout the body, being propelled 

 by the contractile powers of the vessels themselves, and 

 after having supplied the tissues with nourishment, it 

 is carried by tubes to the point from whence it started, 

 to begin a new course. The capillary network passes 

 immediately under a portion of the skin of the star-fish, 

 through which an exchange of the respiratory gases 

 takes place. Besides, the star-fishes breathe the sea- 

 water through numerous conical tubes, that project in 

 patches from the back. Through these tubes, which 

 can be opened and shut, the water is readily admitted 



