WHEEL ANIMALCULES 



1 59 



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 " cilifi," or vibrat- 

 ing hairs of protoplasm.^ 

 These cilia " lash " and 

 straighten again one 

 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 



Fig. 34. — Diagram of Rotifer vulgaris — 

 the common wheel animalcule — one 

 hundred and twenty times as long as 

 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 : M, mouth. 

 W, wheel or ciliated disc. S, eye 

 spots on head. T, spur or tentacle. 

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

 testines. F, vent: aperture of intestine. 



microscope so that the groups or "bunches" of them 



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

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



