26 NOMENCLATURE 



and Enaima of Aristotle those of Myeloneura 

 and Ganglioneura. 



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, Yogt, Yan 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, Peripherie, 



Mollusks, Massive, 



Articulates, Longitudinal, 



Vertebrates. Doubly Symmetrical. 



Though perhaps less felicitous, the names of Baer 

 express the same ideas as those of Cuvier. By 

 the Peripherie type he signified those animals in 



