WHEEL-ANIMALCULES ; HYDATINA. 



323 



the first parts which exhibit motion, they are the last to revive 

 after this kind of resuscitation. 



860. We observe, then, in the Rotifer vulgaris, a very manifest 

 tendency to the Vermiform character, exhibited in the elongated 

 shape of the body, the position of the 

 eyes and mouth at one extremity of it, 

 the narrow, straight, intestinal canal 

 having its second orifice near the other 

 extremity, and the mode of locomotion 

 when the tail is detached and the 

 operation of the wheels suspended. 

 This tendency, however, is not so 

 marked in some species of the class, 

 which are inmanyrespectsmore highly 

 developed than this; for example, 

 the Hydatina senta^ an animalcule 

 not uncommon in vegetable infusions. 

 Here the body is somewhat funnel- 

 shaped ; and the cilia are arranged 

 around the wide mouth, in two con- 

 centric rows. The outer row consists 

 of a simple continuous circle, arranged 

 upon the edge of the body ; but the 

 inner one is made up of eleven groups 

 of cilia, attached to distinct muscular 



lobes. The integument appears to consist, as in the Rotifer, of 

 two membranes, both of which are soft and flexible. To the inner 

 one are attached four pairs of longitudinal muscles, by which 

 the chief movements of the body are performed. The tail has 

 separate muscles for its retraction or protrusion ; and others are 

 seen at the large extremity of the body, which fold up the ciliary 

 apparatus. The distinction between the muscles and the sup- 

 posed vessels is here well marked ; and there can be little doubt 

 that the true function of the latter has been assigned, even 

 though no subdivision or re-union can be traced (on account 

 of the minuteness of the whole object) between the transverse 



FIG. 538. HYDATINA SENTA ; a, 

 rows of cilia ;'Jb, muscles of the ] 

 jaws ; c, stomach ; d, enlarged 

 termination of the intestine ; 

 e, anus ;/, salivary glands ; g, 

 ovaria ; h, dorsal vessel. 



