WHEEL ANIMALCULES 



159 



w 



or a leech fixing itself by its tail, then stretching out the 



head and fixing that, 



whilst letting go the tail 



and bringing it up by 



" telescoping " it, near 



to the head region. The 



tail is forked, and in the 



side view (Fig. 34, B) it 



is seen to have a soft 



branched process, which 



helps it to cling. The 



letter V in Fig. 34, A, 



points to the vent or 



opening of the gut at 



the fork of the tail. 



The mouth, marked 



M, is seen between the 



two " wheels." The two 



"wheels" are really 



two discs, the edges of 



which are beset by 



coarse " cilia," or vibrat- 

 ing hairs Of protoplasm. 1 FlG " 34Diagram of Rotifer vulgaris- 

 r ^ }) the common wheel animalcule one 



1 hese Cilia lash and hundred and twenty times as long as 



Straighten again One the creature itself. A, front view. 



B, side view. C, head showing eyes S, 

 and retracted wheel apparatus W. 

 The letters in A and B have the 

 following signification : Af, mouth. 

 IV, wheel or ciliated disc. S, eye 

 spots on head. T, spur or tentacle. 

 G, gizzard. St, stomach. Int, in- 

 testines. F, vent: aperture of intestine. 



after the other, so that 

 the optical illusion is 

 produced of the toothed 

 edge of the disc being 

 in movement like a 

 wheel. They may be 



"focused" with the 



microscope so that the groups or "bunches" of them 



1 For some account of "cilia," see "Science from an Easy Chair," 

 Figs. 29, 33, 40 and the accompanying text. 



