17f5 



ZOOLOG r. 



Class III. — Rotatoria {Rotifers), 



General Characters of Rotifers.— The Eotifers, or wheel- 

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

 etc., and in the oc(;an, 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. Vii.—Sqnamella Mm.qa, Tnaenifled 200 oMoiiga (Fig. 121), which 



diameters. A view fi-om helow; shell or cara- • „li;pj 4-„ Tirnr-Jtin'niiQ 



pace (s, .«',«');«, the anterior transverse edge ^^ ttiiicu. i^u ^i uoriounai. 



of the carapace; s', the anterior, and «=, ttie TVip fliiirnf'+priat-iV nTCTar\ 



posterior corners of the carapace ;/!Mhe border ^'^^ cnaraCXeriSUC Organ 



or the oval, flat area which occnpies the lower of the wheel-animalculeS 



face of the carapace ; Ih, the cilia-benring velum . 



of the head; C the fork of the; tail «'); m, the is the veluvi (IV) Or pair 

 mouth:.;, jaws;./', muscles which move.;': s*, r. -i- , j i i i-i a 



stomach ; an, the contractile vesicle, or heart of 01 Ciliated Wheel-like oaps 

 the excretory hyetem ; ct;', eifl, the right, and , . , „ , , , , 



CT=, 60<, the left excretory vessels : eg.eg^, eg^, On eacll Side 01 the head, 



two largely developed young.-Af,er Clark. ^j^.^j^ -^ 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, Avith 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. 132). The body is composed of several. 



