82 STUDIES IN ANIMAL LIFE. 



Cuvier, to whom we owe this classification of the 

 animal kingdom into four great divisions, would 

 have been the first to recognize the chaotic con- 

 dition in which he left this last division, and would 

 have acquiesced in the separation of the PROTOZOA, 

 which has since been made. This fifth division in- 

 cludes many of the microscopic animals known as 

 Infusoria, and receives its name from the idea that 

 these simplest of all animals represent, as it were, 

 the beginnings of life.* 



But Cuvier's arrangement is open to a more se- 

 rious objection. The state of science in his day 

 excused the imperfection of classing the Infusoria 

 and parasites under the Eadiata ; but it was owing, I 

 conceive, to an unphilosophical view of morphology 

 that he placed the mollusks next to the Yertebrata, 

 instead of placing the Articulata in that position. 

 He was secretly determined by the desire to show 

 that there are four very distinct types, or plans of 

 structure, which can not by any transitions be 

 brought under one law of development. Lamarck 

 and Geoffroy St. Hilaire maintained the idea of uni- 

 ty of composition throughout the animal kingdom : 

 in other words, that all the varieties of animal forms 

 were produced by successive modifications ; and 

 several of the German naturalists maintained that 

 the vertebrata in their embryonic stages passed 



tern at all ; but the radiate structure is represented in the diagram, 

 as it also is, very clearly, in a Sea-anemone. 



* Protozoa, from proton, first, and zoon, animal. 



