168 THE MICROSCOPE. 



out of sight while the next appears, adding to the optical illusion, a 

 philosopher of considerable note was led to look upon the whole as a 

 deception of the sight, and affirmed they had no existence. The cilia 

 processes appear but in one part of the Rotifera ; whereas in the Vor- 

 ticellidse, cilia are seen in various parts of the body. 



These animalcules are only discovered in water, which is their 

 native element ; still they are found in damp earth, and are indwellers 

 of the cells of rnoss and sea-weed. They possess but one stomach, and 

 generally have teeth and jaws to supply its wants. They can elongate 

 and contract their bodies ; and some species have at their extremity a 

 kind of tail with a sucker, by which they affix themselves to extraneous 

 substances while the cilia is in rapid motion, and thus prevent the su- 

 perior portion of the body being drawn in by the force of the rotatory 

 action. They multiply by eggs j but some bring forth their young 

 alive. Both the animal and its eggs possess extraordinary tenacity of 

 life, and will undergo the most opposite extremes of circumstances 

 without destruction to the living principle. 



In the atmosphere the eggs may often be discovered whirling along 

 by the force of the wind to some resting-place, where, when circum- 

 stances admit, they spring into active life, and fulfil their appointed 

 destiny. Ehrenberg accurately described the upper part of a common 

 wheel-animalcule, with the cilia, jaws, teeth, eyes, as seen under a mag- 

 nifying power of 200 diameters, represented at 1, fig. 101. 



The small arrows show the direction of the currents produced by 

 the cilia turning on their base. At the will of the animal a change is 

 made in the direction in which the wheels appear to revolve, and they 

 have the power of withdrawing, with the quickness of thought, the 

 whole of the wheel-work ; when this is done, the head is elongated, and 

 with a telescopic appearance, as if capable of sliding within itself. On 

 assuming this form, a cluster of hairs appears at the extremity, that 

 do not revolve, and are considered different from the cilia : as they are 

 usually protruded when the creature is moving from place to place, their 

 functions have been imagined to be that of feelers, shown in No. 2. 



The red spots supposed to be the eyes of the Rotatoria are generally 

 of a bright red colour; but the number and arrangement of these organs 

 vary. In some kinds there have been discovered as many as eight, 

 sometimes placed on each side of the head, in a row, in a circle, or in 

 clusters ; and in others, in a triangular shape. 



Ehrenberg, from actual observation, found that the Rotatoria laid 

 four eggs a day ; that the young, when two days old, followed the same 

 law as their parents ; consequently, a single one in ten days had a 



