1 7 2 ECHINODERMA TA. PAKT in. 



into the cavity containing- the digestive organs, with 

 which they are in communication. The star-fish slowly 

 distends itself with water, and then gives out a portion 

 of it, but at no regular time. The cavity is never 

 empty of water, and as its lining is densely bristled with 

 cilia, their vibrations keep the vascular surface of the 

 digestive organs perpetually bathed with the respiratory 

 medium. 



The star-fishes have a radiating system of nerves 

 suited to their form. A ring of slender nerve-cords 

 surrounds the mouth, from whence three nerves are sent 

 off at the commencement of each ray : two of these, 

 which are filaments, go to the organs in the central 

 disk, while the middle one, which is a great trunk, 

 passes through the centre of the rays, and terminates in 

 a nerve-centre, or ganglion, placed under a coloured eye- 

 speck at their extremity. The structure of the rays, 

 the eye- specks, and the nerve-centres below them, are 

 so similar, that they are merely repetitions of one 

 another ; hence no nerve-centre can control the others, 

 but they are all connected by the ring encircling the 

 mouth, which is a common bond of communication. 

 How far the movements of these animals indicate sensa- 

 tion we have not the power to determine, but they feel 

 acutely, for the mouth, the feet, and especially the 

 pedicellarise, are highly sensitive, and shrink on the least 

 touch. The eye-specks are probably sensitive to light, 

 and as the star-fishes often feed on putrid matter, they 

 are supposed to be endowed with the sense of smell. 



The family of the Ophiuridse, or Snake Stars, are 

 widely distributed in the ocean. The genus Euryales 

 with branching rays, and that of Ophiura with simple 

 rays, comprising the Brittle and Sand Stars, are abundant 

 in the British seas. In the sand stars there are cavities 

 full of sand at the points from whence the rays diverge, 

 which appear like warts on the surface of the disk. 



