546 



INFUSORIAL ANIMALCULES. 



known species, far surpassing that of the whole human popula- 

 tion of the earth. 



1202. The forms presented by these Animalcules are ex- 

 tremely various. In some there is a considerable variety in the 

 forms assumed by the same individual under different circum- 

 stances, but still a prevailing shape can be recognised. ID 



FIG. 728. VARIOUS FORMS OF ANIMALCULES. 



others, again, the body, although still unprotected by any firn, 

 envelope, appears to undergo little change in figure, except 

 when affected by some temporary pressure. But there are 

 many species which cannot be influenced even by this; their 

 soft bodies being enclosed in a delicate but firm integument, 

 strengthened by a deposit of silicious matter. These are termed 

 loricated Infusoria ; and these envelopes, which are often pre- 

 served after the death of the animals, are termed their shields or 

 sheaths. 



1203. Although most of the Infusoria have the power of 

 freely moving through their native element, some occasionally 

 attach themselves to a solid base, like Polypes ; but many, like 

 the Hydra and Sea- Anemone, have the power of occasionally 

 detaching themselves, and go in search of a new field for the 

 supply of their voracious appetites. The analogy to the Poly- 

 pifera is very strongly marked in some species, however, in 

 which we not only observe the Animalcules attached during 

 nearly the whole of life, but find a large number associated into 

 one plant-like structure. In all, the body is furnished more or 



