OF THE CLASS INFUSORIA. 489 



OF THE CLASS INFUSORIA, PROPERLY SO CALLED.* 



622. Those animalcules which can only be detected by 

 the microscope, or which, even to a late period, have been con- 

 founded with the rotatoria ( 586), but whose structure is 

 very different, are developed in abundance in water containing 

 the remains of organized bodies. Their body, sometimes 

 rounded, sometimes elongated, is often covered with small 

 cilia, and offers in its interior a number, generally very con- 

 siderable, of small cavities, which seem to perform the func- 

 tions of stomachs. In some, these little enlargements seem 

 to be grouped around a canal which opens externally by 

 two extremities (Fig. 169); but at other times they seem to 

 be altogether isolated ; and persons who have made these 

 little beings the object of a special study, are not agreed as to 

 the existence of a direct communication between this cavity 

 and the exterior. The mode of propagation of the infusoria has 

 been the object of much research, and a great many naturalists 

 think that they may be formed directly by the disintegration 

 of the matters of which leaves, flesh, and other organized 

 bodies are composed ; but this spontaneous generation is far 

 from being sufficiently demonstrated, and it is known that, 

 in certain cases at least, they spring from each other. More- 

 over, their mode of propagation is quite in accordance with 

 the simplicity of their structure : it is by the spontaneous 

 division of their body into two or more fragments, each of 

 which continues to live, and soon becomes a new individual, 

 resembling the first ; thus it is that these singular beings in 

 general multiply. 



Their forms are very varied, and th^y have been divided 

 into several genera, amongst which we may mention the 

 enchelides (in. Fig. 169), which have an oblong body: the 

 volvoces, which are globular, and continually turn on them- 

 sfilves ; and the monades (i. Fig. 169), which resemble small 

 points whirling in the water in which they swim. It is owing 

 to the presence of myriads of a particular species of these 

 small monads, whose bodies are coloured red, that salt stag- 

 nant waters or ditches acquire a sanguinolent colour. 



* Many of the small beings which zoologists place in this group appear 

 rather to belong to the division mollusca than to that of zoophytes ; but 

 their natural affinities have not as yet been so clearly established as to enable 

 us to discuss this question here. 



