EOTATORI^. 



167 



are generally the Monads, which in a very short period increase to a 

 most extraordinary extent. These afterwards gradually decrease, larger 

 and more perfect creatures supplying their place, as the Peridinida, 

 Paramesia, Trachelina, Acineta, and others; and these, again, are sup- 

 planted by the Vorticellae and Branchionsea. Though the generations 

 thus rise up, there is no regular order in their doing so, even in the 

 same infusions. 



THE EOTATOEI^, ROTATING OR WHEEL-ANIMALCULES, 



This higher grade of the Infusoria, now classed among the Articil- . 

 lata, derives its name, from the appearance presented by the motion of 

 its circles of cilia on the superior part of its body, which resembles the 

 turning round of a wheel, as tkey rapidly vibrate. Many have been 



fig. 101. 



1 The common Wheel- AnimaTdule, witt its cffia or rotators pointea. 2. The same 

 in a contracted state at rest: &t g is seen the development of the eyes in the 

 young. 3. Pitcher-shaped -Braohionus : a the jaws ; i the sheU ; c the cUia, or 

 rotators ; d the tail. 4. Baker's Braohionus : a the jaws and teeth ; 6 the sheU ; 

 e the rotators ; e the stomach. 5 and 6. Other forms of the same family. 



the speculations as to the mechanism of this beautiful movement: some 

 have considered it as a, magnetic or electrical force; and as one passe* 



