No.- 19.] ECHINODERMS OF CONNECTICUT. 99 



passes out at an opening on the summit of the body, in the 

 small area where all the zones converge. The rejected particle 

 is received on one of these little forks, which closes upon it like 

 a forceps, and it is passed on from one to the other, down the 

 side of the body, till it is dropped off into the water. Nothing 

 is more curious and entertaining than to watch the neatness and 

 accuracy with which this process is performed. One may see 

 the rejected bits of food passing rapidly along the lines upon 

 which these pedicellarise occur in greatest number, as if they were 

 so many little roads for conveying away of the refuse matters; 

 nor do the forks cease from their labor till the surface of the 

 animal is completely clean, and free from any foreign substance. 

 Were it not for this apparatus the food thus rejected would be 

 entangled among the tentacles and spines, and be stranded there 

 till the motion of the water washed it away." 



In the purple urchin the aboral area is devoid of spines, and 

 so smooth that refuse matter or foreign particles which fall upon 

 it will be easily washed away by currents of water or by the 

 movements of the animal. 



In the disk-urchins the intestinal opening is placed at the edge 

 of the disk or on the lower surface, so that the fecal matter 

 does not fall upon the body. Furthermore the spines are covered 

 with cilia, and these create a current of clean water which con- 

 stantly flows past the animal and washes away any very minute 

 foreign particles. The movements of the minute spines and tube- 

 feet brush away any particles which are not thus removed. 



Food. — The regular urchins feed largely upon seaweeds, but 

 also devour any dead animal matter obtainable and supplement 

 their diet by the diatoms and such other minute organisms as 

 are found upon the bottom on which the animals live. Much 

 sand and mud is swallowed for the organic matter in it. The 

 disk-urchins swallow great quantities of sand, with such diatoms 

 and other minute organisms as it contains. 



Natural enemies. — Many kinds of fishes feed upon all our 

 species of echinoids, in spite of their covering of spines, and the 

 free-swimming embryos are subject to the attacks of still other 

 species of fishes. 



