26 NOMENCLATURE 



and Enaima of Aristotle those of Myeloneura 

 and Gangliuneura. 



But it is not my object to give all the classifica- 

 tions of different authors here, and I will there- 

 fore pass over many noted ones, as those of Bur- 

 meister, Milne-Edwards, Siebold and Stannius, 

 Owen, Leuckart, Vogt, Van Beneden, and others, 

 and proceed to give some account of one investi- 

 gator who did as much for the progress of Zoology 

 as Cuvier, though he is comparatively little known 

 among us. 



Karl Ernst von Baer proposed a classification 

 based, like Cuvier's, upon plan ; but he recognized 

 what Cuvier failed to perceive, — namely, the 

 importance of distinguishing between type (by 

 which he means exactly what Cuvier means by 

 plan) and complication of structure, — in other 

 words, between plan and the execution of the 

 plan. He recognized four types, which corre- 

 spond exactly to Cuvier's four plans, though he 

 calls them by different names. Let us compare 

 them. 



Cuvier. ■■ Baer. 



Radiates, Peripheric, 



Mollusks, Massive, 



j Articulates, . Longitudinal, 



Vertebrates. Doubly Symmetrical. 



Though perhaps less felicitous, the names of Baer 

 express the same ideas as those of Cuvier. By 

 the Peripheric type he signified those animals in 



