176 



ZOOLOO T. 



CLASS III. ROTATOTUA (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 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 revived 

 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 



Fig. \2\.-SqnamfMa ot>lf>nr,a, magnified 200 ollongci (Fig. 121), which 



is allied to Brachionus. 



s 



eg 



cv 3 



cv* 



diameters. A view from lielow; shell or cara- 



pace (s, ', s s ); s, the anterior transverse edge 



of the carapace; s 1 , the anterior, and * 2 , the r ri-,p plviviprnricrir' r>rrran 



posterior corners of the carapace ; .s", the border 31gan 



of the oval, flat area which occupies the lower O f the wheel-animalcules 



face of the carapace ; lf>, the cilia-bearing velnm 



of the head; /, the Cork of the tail ((I 1 ); m.the is the Velum (lb] Ol* pail 1 



mouth -j, jaws ; ,/', muscles which mo\ej;ft, -i 1-1 



stomach ; cv, the contractile vesicle, or heart of OI Ciliated wheel-like flaps 



the excretory system ; c?; 1 , rw 2 , the right, and , . -, ., , , 



cv 3 , cv*, the left excretory vessels; eg,~tg*, eg*, On each Side OI the head, 



two largely developed young. After Clark. i i 11 



which is comparable to 



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



