Lefevre — The Advance of Zoology in the Nineteenth Century. 81 



It may be mentioned here that the embryologist Von Baer 

 (1792-1876) adopted Cuvier'sfour divisions, calling them the 

 Vertebrate, the Massive, the Longitudinal, and the Peripheric, 

 and believing that the same unity in plan of structure could 

 be recognized in the development of each group. 



In Cuvier's mind the identity of plan existing throughout 

 a group is the expression of an idea of the Creator, and not 

 only is the species a fixed and permanent reality but the type 

 as well. He vigorously combatted the speculations of the 

 nature-philosophers regarding the transformation or evolution 

 of forms ; while the variation of the details of structure within 

 a single type, with the retention of the essential plan, was to 

 him merely evidence of the Creator's consummate skill. He 

 was led into bitter controversy with his opponents, or those 

 who held to the transmutability of species, the conflict reach- 

 ing its climax in the famous dispute in the French Academy 

 between Cuvier and St. Hilaire, the leader of the French 

 nature-philosophers. This discussion took place in 1830 and 

 lasted through several sessions, the result being that Cuvier 

 through his greater authority and much wider knowledge of 

 comparative anatomy completely vanquished his antagonist. 

 The victory thus won by Cuvier, by force of arms as it 

 were, for the immutability of species and fixity of plan in 

 nature, completely dominated the study of zoology until Dar- 

 win's time, and feeble were the efforts made to dislodge it 

 during the intervening thirty years. The last serious advo- 

 cate of Cuvier's types was Louis Agassiz, who held the rare 

 distinction of being the only naturalist of prominence to re- 

 ject the doctrine of descent and who until his death remained 

 a bitter opponent of Darwin. 



Foremost among Cuvier's disciples may be mentioned Rich- 

 ard Owen who carefully dissected and studied many animals, 

 both vertebrate and invertebrate, including a number of very 

 rare forms, such as the Pearly-Nautilus and the New Zealand 

 Apteryx. He especially concerned himself with the recon- 

 struction of extinct vertebrates, following the Cuvierian 

 method founded on the principle of correlation of parts. 

 The terms homology and analogy are due to Owen, who 

 rendered zoology an inestimable service by clearly and 



