ECHINODERMATA. 139 



under his superintendence, and which now constitute 

 part of the comparative anatomy collection of the 

 University of Edinburgh. He was particularly suc- 

 cessful in his injections of the water-vascular system 

 of those animals, specimens of which he exhibited to 

 the "Wernerian Society in 1846, and was led therefrom 

 to agree with those authorities who considered that the 

 vascular and water- vascular systems were not distinct 

 and independent, but parts of one great vascular 

 system connected together into one system by 

 communications. For he found that when an in- 

 jection was forced into the water-vascular system of 

 tubes, it did not confine itself to them, but passed into 

 and distended the other systems also without any 

 rupture of vessels. He believed that in the sea- 

 urchins, the blood moved in various directions without 

 any regular current, and that the direction was in- 

 fluenced by circumstances. For these animals have 

 several series of ambulacral holes and protrusible feet, 

 and his injections of the system of vessels provided for 

 the protrusion of the feet, displayed fine vessels passing 

 along each ambulacral segment which did not pass 

 directly into the inner part of the suckers, but first 

 subdivided into a double series of triangular lamina*, 

 or vascular plates arranged on each side of the am- 

 bulacral holes. These vascular laminae contain a very 

 rich n«t work of vessels, from which the feet procure 

 the fluid by which they wire distended in the in- 

 jections. 



lie described, with great care, from observations 



