134 



ZOO LOO T. 



CLASS III. ROTATORIA (Rotifers'). 



General Characters of Rotifers. The Rotifers, 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 hundred ths 

 of an inch in length (f 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 

 j\ dried for months to such 

 g a degree that little if any 

 eg moisture is left in the 

 ^,3 body, they may be revived 

 and become active. Pro- 

 fessor Owen has observed 

 c& the revivification of a 

 Rotifer after having been 

 eg kept for four years in dry 

 sand. 



As an example of the 

 ordinary type of Rotifer 

 we may cite Squamella 



Fig. 91. -Sqimmella oMcmc,a, magnified 200 oUonga (Fig. 91), which 

 diameters. A view from below; shell or cara- 

 pace (s, .'. - 2 ) ; s, 'he anterior transverse edge 

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

 posterior corners of the carapace; x :f , the border 

 of the oval, Hat area winch occupies the lower 

 face of the carapace: Ib, the cilia-bearing velum 

 of the 

 mouth 

 stoinac 

 the 



^3 



two largely developed young. After "Clark. ^-1,;,,]. Pm -n-il 



\* 111^11 1O \j\JLLl L/ttl Cb*J\.\j \J\J 



the velum of the larval mollusk. By means of the rotatory 

 movements of this velum the creature is whirled swiftly 

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

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

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

 Rotifer vulgar is (Fig. 9'3). The body is composed of several, 



is allied to Brachionus. 

 The characteristic organ 

 of the wheel-animalcules 



