176 



ZOOLOGY. 



Class III. — Rotatoeia {Rotifers). 



cv* 



«?> 



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

 animalcnles, are abundant in standing ivater, in damp moss, 

 etc., and in the ocean, and ai'e 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 (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 

 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 

 Eotifer after having beea 

 kept for four years in dry- 

 sand. 



As an example of the 

 ordinarj- type of Eotifer 

 we may cite Sqiianiella 



ms. m.—StptumeOa oblont/a, magnlfled 200 oUonga (Fig. 131), which 



diameters. A view from liplow; shell or cara- ■ Qiii«/J f^ Tivtml 'r, 



pace (s, j*i, n"^) \ s, rhe antorior transveree edge ^° tliueu tO HTUClllOTlUS* 



of rhe carapace ; .■ii, the anterior, and ifl. the ^y\xn r'li.jn-oofQvic.fi/i rvi./vnn 



posterior corners of the carapace ; k3_ ihe border ^^^ oudiauuei tbUC orgaH- 



or the oval, flat area which occnpies the lower of tlip Tv-l-iool nnimal/inl/ic. 

 faceof the carapace: », the cilia-hearing velnm '' ^^^ "neei animaiCUies 



of thehead; H, theforkof the tail ((>); m.Ihe is the Velum (lb) Or -nair 

 month ; J, jaws ;.;', muscles which move,?:^^, n -i. 



stomach ; a\ the'contractile vesicle, or heart of of Ciliated wheel-like flaps 

 the excretory hysteni ; cv^, cn^, the right, and , . , - . '■ 



cv^.ci''. the Jea excretory vessels ; eg/e^Keg', OU eaCU Side 01 tlie head, 

 two iareely developed young, — After Clark. , . , . -, -, , 



which IS comparable to 

 the velum of the larval niollusk. By means of ihe rotatory 

 movements of this velum the creature is whirled swiftly 

 around. The body is broiid and flattened, with the ^\alls 

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

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

 Eotifer vulgaris (Pig. 192). The body is composedof several^ 



