74 ETIENNE GEOITROV SAINT-HILAIUE 



could not be compared directly, bone for bone, with the 

 skeleton of higher Vertebrates; he had to admit differences 

 of position of whole sets of organs in the two groups, 

 he had to admit various wctastases, before he could bring 

 the skeleton of fish into line. And these metastases are 

 due to functional requirements for example, the forward 

 position of sternum and thoracic organs in fish is an 

 adaptation to swimming. 



So he does not so much demonstrate the unity of plan 

 of whole organisms as the unity of plan of particular 

 corresponding parts of them. Thus he does not prove or 

 attempt to prove that Articulates are in all points like 

 Vertebrates, but simply that their skeleton is built upon 

 the same plan as that of Vertebrates. The rest of the 

 organs, while still comparable with the organs of Verte- 

 brates, stand in different relations to the skeleton. 

 An Articulate therefore, on his own showing, is not, as 

 a whole, built upon the same general structural plan as a 

 Vertebrate. 



Further, he does not always remain true to his principles, 

 for he does not establish homologies of parts entirely by 

 their connections but sometimes by their functions as well. 

 Thus the sternum, or rather the complex of sternal elements, 

 is defined and discovered in particular cases not by its 

 connections only but also by its functions. The framework 

 of the gills is homologised part by part with the framework of 

 the lungs, not because the relations of the framework to the 

 rest of the skeleton are the same in fish and air-breathing 

 Vertebrates, but simply because gills are considered the 

 equivalents of lungs a comparison which is purely 

 physiological. 



Even with these concessions to the functional view of 

 living things, Geoffroy was unable to make good his 

 contention that all animals are built upon the same plan. 

 His arguments failed to carry conviction to his con- 

 temporaries, and Cuvier in particular subjected them to 

 destructive, and indeed final, criticism. 



The paper, already referred to, in which Cuvier disposed 

 of the transcendentalists' comparison of Cephalopods and 

 Vertebrates is of great significance, for it states in the 



