SOME AQUATIC WORMS, ETC. l8l 



The food consists of the niinute particles of decayed 

 animal and vegetable matter so abundant in the soft 

 •surface of the mud at the bottom of our shallow ponds. 

 These particles are taken in with a peculiar and a sud- 

 den snapping movement of the cavity of the oesopha- 

 gus, easily to be seen but difficult to describe. Dia- 

 toms are rarely swallowed. 



So far as their classification is concerned, these at- 

 tractive little animals have given naturalists a good 

 deal of trouble. Some have said that they belong 

 with the Rotifers; others have placed them among the 

 Infusoria; others have called them low worms, putting 

 them among the Turbellaria; and still others think, 

 and they are doubtless correct, ' that Chaetonotus 

 should stand in a group by itself, among the worms, 

 and not very far from the Rotifers, the group to be 

 named the Gastrotricha. 



They are all rapid swimmers, and on that account 

 are rather difficult to study, but by following one for 

 a little while, it will usually be seen to settle down and 

 begin to seek food, and that is the observer's oppor- 

 tunity, unless he desires to kill the specimen, and study 

 it after death, a procedure that is seldom satisfactory. 



The following Key leads to some of our common 

 forms : 



Key to Species of Chcetonotus and to its Allies. 



§ Posterior extremity forked {A). 



§ Posterior extremity not forked but bearing several 

 long, coarse bristles, Dasydytes. i. 



A. Upper surface without spines, prickles or scales, 

 (a). 



A. Upper surface having scales, spines, spinous 

 scales or prickles, (f). 



