NO. 19.] ECHINODERMS OF CONNECTICUT. I23 



contact with any particles of organic substance or small organ- 

 isms which may be present. Such materials may then be grasped 

 by one of the tentacles, which is then withdrawn into the mouth, 

 and the adhering particles collected are scraped off to serve as 

 food. The tentacle is then thrust out for further exploration. 

 In such a manner quantities of mud containing more or less nutri- 

 tive substance pass into the alimentary canal. 



When living in sand, however, the animal is able to select the 

 food materials and reject most of the particles of sand. Even 

 when sand particles are conveyed into the mouth they are often 

 brought out again when the tentacle returns in search of more 

 food. The tentacles take their turn in conveying the food, and 

 as a rule only a single tentacle enters the mouth at one time. 

 Another tentacle may bring its catch near the mouth and wait 

 for the first tentacle to be withdrawn before entering. An exam- 

 ination of the stomach contents shows the food to consist of 

 protozoans, small worms, Crustacea and other animals, together 

 with diatoms, unicellular and filamentous algae and fragments 

 of other plants and animals. 



The respiratory movements involve the whole body, the body 

 walls expanding and contracting as the water is taken in and 

 expelled from the cloacal opening. The discharged water often 

 forms a jet of some force. 



In its natural position, the common Thyone lies with the 



cloacal aperture widely opened and slightly elevated above the 

 surface of the sand or mud. Through this opening water is alter- 

 nately pumped into the cloaca and the respiratory trees and 

 forcibly expelled. This act of respiration often occurs with a 

 fairly definite rhythm, at intervals varying under different con- 

 ditions from 15 seconds to more than a minute. The anterior 

 end of the animal mav also lie at the surface of the mud, with 

 the main portion of the U-shaped body concealed beneath the 

 surface. From time to time the animal buries also the anterior 

 end and remains for hours with only the tip of the cloaca pro- 

 jecting. If disturbed, there is a sudden jet of water forced from 

 the cloaca, and the end of the body is withdrawn beneath the 

 surface. Even a shadow falling upon the sensory papillae sur- 

 rounding the cloacal opening is sufficient to cause this reaction. 

 If placed upon the surface of the sand the animals may either 



