INFUSORIA — CILIA. 405 



being performed at the same time, the motion of the 

 organs that propels it forward causing a current to set 

 towards the mouth, which carries with it the prey on 

 which the animal feeds. From the cilia being found in 

 the gills of the young tadpole, the oyster, and mussel, it 

 would appear that they are serviceable as organs of respi- 

 ration, by imbibing oxygen, and emitting the carbonic acid 

 generated in the blood during its circulation through the 

 body; they are also believed to be the medium of taste 

 and touch. It is not only at the mouth, but over the 

 whole body that cilia are discovered ; and it is now satis- 

 factorily shown that cilia exist also in the internal organs 

 of man and other vertebrated animals ; and are agents 

 by which many of the most important functions of the 

 animal economy are performed. They vary in size from 

 the 1000th to the 10,000th of an inch in length. These 

 minute organs would often be invisible, were it not from 

 the water being coloured when placed under a microscope ; 

 then the little currents made by the action of the cilia are 

 easily perceived; and when the water is evaporated, the 

 delicate tracing of their formation may be observed on the 

 glass. They are differently placed, and vary in quantity 

 in the numerous species of Infusoria. In some they are 

 in rows the whole length of the body, in others on the 

 base ; many have them over the whole of the body ; some- 

 times they fringe the mouth, form bands around projec- 

 tions on the body ; and many have but two projecting 

 from the mouth, as long as the body of the creature. 

 Ehrenberg says they are fixed at their base by the bulb 

 moving in a socket, in a similar manner to a man's out- 

 stretched arm; and by their moving round in a circle, 

 they form a cone, of which the apex is the bulb. Poison, 

 galvanism applied to the animal, even death, will not im- 

 mediately stop the motion of the cilia ; they continue 

 moving some hours afterwards, even longer than nervous 

 or muscular action can be sustained, until the fluids dry 

 up, and they stiffen. 



Very little is known of the muscular attachment of cilia 

 in Infusoria ; but the motive power must be derived from 

 muscular structure in all. Now in the wheel-animalcules 

 the cilia are in circular rows ; and each revolves around 



