WHEEL ANIMALCULES. 189 



natural to suppose that a texture analogous to 

 that of muscles might exist in these latter genera 

 of infusoria. It was not till very recently, how- 

 ever, that the actual presence of contractile fibres 

 could be recognised. But this problem has at 

 length been solved by the discoveries of Ehren- 

 berg, who, in his observations of the larger and 

 more highly organized species belonging to the 

 order of Rotifera, has, with a magnifying power 

 of 380, distinctly seen muscular bands running 

 in pairs between the two layers of transparent 

 membrane which envelope the body. When the 

 animalcule throws itself into its violent lateral 

 contortions, these fibrous bands are observed to 

 become broader and thicker, as well as shorter, 

 on the side towards which the contractions take 

 place. There can, therefore, be no doubt that 

 these are muscular organs, and that they are the 

 real agents by which the motions witnessed are 

 effected. 



These Rotifera, or wheel animalcules, are so 

 R named from their being provided 

 80 ^^Blk w * tn an a PP ar ^tus for creating a 

 perpetual eddy, or circular cur- 

 rent in the surrounding fluid. 

 The remarkable organs, by which 

 this effect is produced, are gene- 

 rally two in number, (Fig. 80, R, R) 

 and are situated on the head, but 

 do not surround the opening of 

 the mouth, as is the case with the tentacula of 



