542 POLYGASTRIC ANIMALCULES. 



almost any figure. In others there is still considerable variety 

 in the forms assumed by the same individual under different cir- 

 cumstances (Fig. 626, d) ; but still a prevailing shape can be 

 recognised. In others, again, the body, although still unprotected 

 by any firm 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, strength- 

 ened by a deposit of siliceous matter. These are termed loricated 

 Infusoria ; and these envelopes, which are often preserved after 

 the death of the animals, are termed the shields or sheaths. 



1116. Although most of the Polygastrica 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 almost all the Polygastrica, we 

 find the body furnished more or less abundantly with cilia, which 

 serve various important purposes. Sometimes they are only 

 disposed around the mouth, towards which they produce a vortex 

 of fluid, that brings a supply of alimentary particles. Where the 

 digestive cavity has a separate termination, this also is usually 

 fringed with cilia, by the action of which the particles rejected 

 are thrown off to a distance. And, in many of the higher species 

 not enclosed in a siliceous envelope, the whole body is beset with 

 rows of these little filaments ; by the action of which every pos- 

 sible variety of movement seems to be produced. 



1117. The name Polygastrica has been applied to these 

 Animalcules by Ehrenberg, in consequence of his belief that 

 they possess a large number of distinct stomachs, or cavities for 

 the reception and digestion of aliment. This belief is founded 

 on the appearance which many of them present, when they have 

 been allowed to remain for a short time in water, in which finely 



