ROTATOR!^. 333 



through the water. Their increase is both by eggs and 

 self-division ; and the various families are unlike in size, 

 shape, and colour ; usually of about the hundredth part 

 of an inch in size. When found they resemble a mass 

 of green jelly encircling a twig ; and often, while swim- 

 ming, they take the form of a cup, having the tail 

 drawn within their body. 



Stentor Cceruleus, "Blue stentor," is remarkable from 

 having a crest extending along its body; it assumes a pe- 

 culiar shape when swimming, appearing to possess a thick 

 tail nearly one half the breadth and length of its body. 

 We may here notice a peculiarity with regard to animal- 

 cules procured from infusions ; in the first place, life 

 appears generally in the Monad form, which in a very 

 short period increase to a most extraordinary extent. 

 These afterwards gradually decrease, larger and more 

 perfect creatures supply their place, &sfinchelia, Peridincea, 

 Paramecia, Trachelina, Euplota, with others ; and these, 

 again, are supplanted by Vorticellidce, rachioncea, &c. 

 The changes do not always occur in the order above indi- 

 cated, even in the same infusions. 



KOTATORLE, ROTATING OR WHEEL ANIMALCULES. This 



class of Ehrenberg's Infusoria are now placed among the 

 true Annulosa, and derive their name from the appearance 

 presented by the motion of circles of cilia on the superior 

 part of its body, which resemble the turning round of a 

 wheel on its axis. Many have been the speculations 

 as to the mechanism of this beautiful movement: some 

 have considered it as a magnetic or electrical force; and 

 as one passes out of sight while the next appears, adding 

 to the optical illusion, a philosopher of considerable note 

 was once led to look upon the whole as a deception of sight, 

 and affirmed that the wheels had no existence : they appear 

 only in the head or upper part of the Eotifera. 



Wheel- animalcules are generally found in water, which 

 is their native element ; sometimes they are indwellers of 

 the cells of moss and damp weed. They possess but one 

 stomach, and generally have teeth and jaws to supply its 

 wants. They can elongate and contract their bodies ; and 

 some species have their extremity prolonged to a tail with 

 a sucker; others have a forked process, by which they 



