176 



ZOOLOO T. 



CLASS III. ROTATORIA (Rotifers). 



General Characters of Rotifers. The Kotifers, or wheel- 

 animalcules, are abundant in standing water, in damp moss, 

 etc., and in the ocean, and are so transparent that their in- 

 ternal anatomy can be studied without dissection, while they 

 are so minute, being from one fortieth to three hundredths 

 of an inch in length (^ to f mm.), that high powers of the 



microscope are needed in 

 studying them. They are 

 of special interest from 

 the fact that after being 

 dried for months to such 

 a degree that little if any 

 moisture is left in the 

 body, they may be 1'evived 

 and become active. Pro- 

 fessor Owen has observed 

 the revivification of a 

 Rotifer after having been 

 kept for four years in dry 

 sand. 



As an example of the- 

 ordinary type of Rotifer 

 _ we may cite Squamella 



" mmdln Mnw. magnified 200 ollonga (Fig. 121), which 



is allied to 



35 



of the carapace ; ,', the anterior, and *- 2 . the 

 posterior corners of the carapace; * 3 , the border 

 Of the oval, flat area which occupies the lower 

 face of the carapace: Ik, the cilia-hearing velum 

 of the head; t, the fork of the tail (/') ; m, the 

 mouth ; j, jaws ; /', muscles which move j; St. 

 stomach ca, the' contractile vesicle, or heart of 



The characteristic organ 

 of the wheel-animalcules 



is the velum (11} or pair 

 of ciliated wheel-like 



, 



on each side of the head, 

 which is comparable to 

 By means of the rotatory 



two largely developed young. After 'Clark. 



the velum of the larval mollusk. 

 movements of this volnm the creature is whirled swiftly 

 around. The body is broad and flattened, with the Malls 

 often dense, chitinons, sometimes shell-like, and variously 

 sculptured, or the animal may be long and worm-like, as in 

 Rotifer vulgaris (Fig. 122). The body is composed of several^ 



