262 



THE FOOD OF ANIMALS 



tation, especially mosses, but some are to be found in brackish 

 water or in the sea. They present a great variety in form and 

 habit; the majority are free-swimming, but others live in tubes 

 constructed by themselves, and others again are parasitic. A 

 typical free - living form has elsewhere been briefly described 

 (vol. i, pp. 434, 435). In by far the greater number food is brought 

 to the mouth by ciliary action, set up by variously-arranged cilia 

 placed on the front end of the body and sometimes situated on. 

 special lobes. The name "wheel-animalcule" was given by early 

 observers, who studied species in which there are two circlets of 

 cilia placed on adjacent projections. The successive movement 

 of the cilia on these projections produces an optical illusion, and 

 suggests the movement of a wheel. Thus, Baker, writing about 

 1744 to the then President of the Royal Society concerning his 

 observations on the form already described, the Rose-coloured 

 Rotifer (Philodina roseola] (see vol. i, p. 434), gives the following 

 account, which, though it mistakes the nature of the " wheels", 

 which is not surprising, clearly grasps their use 

 in feeding: " If the water standing in gutters 

 of lead, or the slimy sediment it leaves behind, 

 has anything of a red colour, one may be almost 

 certain of finding them therein, and, if in sum- 

 mer, when all the water is dried away, and 

 nothing but dust remains, that dust appears 

 red, or of a dark-brown, one shall seldom fail, 

 on putting it into water, to discover multitudes 

 of minute reddish globules, which are indeed 

 the animals, and will soon change their appear- 

 ance in the manner just now mentioned. . . . 



"A couple of circular bodies, armed with 

 small teeth like those of the balance-wheel of a 

 watch, appear projecting forwards beyond the 

 head, and extending sideways somewhat wider 

 than the diameter thereof. They have very 

 much the similitude of wheels, and seem to turn 

 round with a considerable degree of velocity, by which means a 

 pretty rapid current of water is brought from a great distance to 

 the very mouth of the creature, who is thereby supplied with many 

 little animalcules and various particles of matter that the waters 

 are furnished with." 



Fig. 470. Crown Rotifer 

 [Stephanoceros], enlarged 



