98 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



to be able to move rapidly without making any use of the tube- 

 feet, and the latter to walk with the tube-feet exclusively without 

 touching the spines to the object on which they are moving. The 

 sand-dollar and key-hole urchin move through -the sand by the 

 actions both of the minute spines and of vast numbers of suck- 

 ing tube-feet on both upper and lower surfaces of the disk-like 

 body. These hundreds of tube-feet attach themselves to the 

 particles of sand, and by their combined action draw the body 

 forward, the minute spines aiding in the process. 



The regular urchins can easily right themselves from any 

 position in the water by the combined action of tube-feet and 

 spines. The disk-urchins, on the other hand, can only right 

 themselves after they have buried their bodies in the sand. 



Locomotion in any direction is accomplished with equal ease 

 by the regular urchins, while the disk urchins ordinarily move 

 with the portion of the disk which bears the intestinal opening 

 backward. 



The behavior of various species of echinoids under a great 

 variety of conditions has been studied extensively by numerous 

 investigators. In the popular book by Romanes,* and in a recent 

 book by Von UexkuU,f may be found most interesting accounts 

 of the performances of these fascinating creatures. 



The bodies of all species must be kept clean, and for this 

 purpose special provision is made. In both the green and the 

 purple urchin the intestinal opening is in the center of the upper 

 surface. Consequently when the refuse matter is discharged it 

 tends to fall directly upon the surface of the body. In the green 

 urchin this region is thickly studded with minute movable spines 

 and pedicellari?e which can be moved in such a way as to pass 

 any foreign particles from one to the next nearer the border of 

 the test, so that such particles are quickly cast away from the 

 body. The tube-feet also aid in the cleaning process. 



Elizabeth and Alexander AgassizJ describe this action of the 

 pedicellariae in the following words : — "If we watch the sea- 

 urchin after he has been feeding, we shall learn at least one of 

 the offices which this singular organ performs in the general 

 economy of the animal. That part of his food which he ejects 



* Jellyfish, Starfish, and Sea-Urchins. 



t Umwelt und Innenwelt der Tiere. 



+ Seaside Studies in Natural History, page 105. 



