PEIMAEY DIVISIONS AND CLASSES. 215 



sensibility and power of motion, but become so degraded as 

 to resemble nothing in the animal kingdom. 



Finally, most naturalists also arrange in the division 

 zoophytes, a fifth group, composed of an infinite number of 

 beings, extremely small (Fig. 169), which live in stagnant 

 waters, and are called infusoria animalcula. They move by 

 means of their vibratile cilia, and strongly resemble in 

 general the larva? of sponges (spongiariae), of polyps, and of 

 the acalepha ; but they do not change as they grow up, and 

 they are remarkable for their fissiparous reproduction, and 

 for the considerable number of stomachs hollowed out in the 

 interior of their bodies for the reception of food. These 

 beings until very lately were confounded with the systolides, 

 under the common name of microscopic animalcules or in- 

 fusoria, and in order to distinguish them they were often 

 called polygastric infusoria. The place they ought to 

 occupy in our zoological classifications has not as yet been 

 well determined. 



Pig. 169. Infusoria.' 



Such are the more prominent characters of the principal 

 organic types of tne animal kingdom. The sketch just given 

 will suffice to give the reader a general idea of the modi- 

 fications introduced by nature into the structure of animated 

 beings-; but to limit our view to this would lead to extremely 

 imperfect ideas of the true nature of zoology. It becomes 

 necessary, therefore, to examine more carefully each of the 

 great divisions corresponding to these fundamental differ- 

 ences. The subjoined tabular view, representing a synoptic 

 table, will assist the reader in comprising at a glance the 

 basis of the classification adopted in this work. 



* Various polygastric infusoria, seen under the microscope : i, monads ; 

 ii, trachelia anas ; in, enchelis, represented at the moment when rejecting 

 the residue of the food ; iv, paramecia; v, kolpod; vi, trachelia fasciolata, 

 marching on microscopic vegetables. 



