72 THOUGHTS ON ANIMALCULES. 



The family to which they belong* comprises the Roti- 

 fers which are furnished with a pair of simple, nearly 

 circular, wheel-like rotators. The body is either cylin- 

 drical, fusiform (spindle-shaped), or vermiform, with- 

 out a case or sheath, but capable of contracting into a 

 globular mass by the involution or withdrawal of the 

 upper part of the body into the lower, somewhat after 

 the manner of a telescope. There are many species, 

 which are arranged in seven genera; most have eyes, 

 and discernible internal muscles. The species before 

 us (pi. xn) will suffice to afford a full illustration of 

 the organisation of this interesting group of animal- 

 cules ; and as it is abundant in every pool and stream, 

 in every phial containing water with decomposing vege- 

 tables, and may even be obtained from the dry sedi- 

 ment in leaden troughs, the reader, whose curiosity is 

 awakened by the following remarks, may readily pro- 

 cure specimens for examination. 



The COMMON WHEEL-ANIMALCULE, (Rotifer vulgaris, 

 pi. xn, fig. 3), is from one-quarter to one-half of a line in 

 length: its body is of a whitish colour and fusiform shape, 

 that is, largest in the middle, and tapering towards the 

 ends, the tail part being the smallest. In the middle of 



* Philodinea of Ehrenberg. 



