194 MICROSCOPY FOR BEGINNERS. 



row of clusters on each side of the lower surface of the 

 body. The spines are slightly curved, long and forked, 

 the bristles being three times their length. The mouth 

 is triangular. The blood is bright red and the vessels 

 large. The body is thread-like, transparent, 

 and may be from one to two inches in length. 

 The front end is whitish, the tail end yellow- 

 ish. It lives in the mud beneath shallow 

 Fig. 139. PO- water, and buries itself with about two-thirds 

 and bristles ^ * ne tail end protruding and constantly vi 

 or strephu- brating. When disturbed it disappears into 

 its burrow with astonishing rapidity. Dr. 

 Leidy, who discovered this curious creature, says, " While 

 walking in the outskirts of the city [Philadelphia] I no- 

 ticed in a shallow ditch numerous reddish patches of 

 from one to six inches square, which, supposing to be a 

 species of alga, I stooped to procure some, when to my 

 surprise I found them to consist of millions of the tails 

 of Strephuris dgilis, all in rapid movement. The least 

 disturbance would cause a patch of six inches square so 

 suddenly to disappear that it resembled the movement 

 of a single body." 



8. -2EOLOSOMA. 



The bristles are of unequal length, and are arranged 

 in clusters of four bristles each, the clusters forming a 

 single row on both sides of the body. There are none 

 in advance of the mouth, which is large U-shaped, the 

 arms of the TJ pointing forward, the whole being sur- 



