HISTORY OF THE SOCIETY. 479 



" What is most remarkable in all the fishes inferior to the 

 oolitic series, besides their analogy with reptiles, is, on the one 

 hand, the very great uniformity of the types, and, on the other, 

 the very great uniformity of the parts of the same animal among 

 themselves ; so that it is often difficult to distinguish the scales, 

 the bones, and the teeth, from one another. If we may be per- 

 mitted to hazard some conjectures on this state of things, such 

 as it is presented to us now, we are naturally led to think, that 

 the principle of animal life, which developes itself at a later pe- 

 riod under the form of ordinary fishes, reptiles, birds, and mam- 

 miferous animals, is at first entirely confined to those singular 

 sauroid fishes which partake at the same time of the structure of 

 fishes and reptiles, and that this mixed character is never lost in 

 this class till the appearance of a larger number of reptiles, in 

 the same manner as we see ichthyosauri and plesiosauri partaking 

 in their osteology of the characters of the cetacea, and the large 

 land saurian animals partaking of the characters of the pachy- 

 derma, which were not created till a much later period. 



" We are thus led by observation to those ideas of the philo- 

 sophy of nature which have presented us with an organic and 

 regular development in all created beings, constantly in confor- 

 mity with the different conditions of existence which are realized 

 at the surface of the globe, in consequence of the changes which 

 it itself has undergone. 



" As a result of all the facts I have brought forward, I distin- 

 guish, in the whole series of geological formations, two grand 

 divisions, which have their limit at the green-sand deposit. The 

 first, the more ancient, includes only the Ganoldes and Placo'i- 

 des. The second, more intimately connected with beings at 

 present in existence, includes forms and organizations much more 

 diversified ; these are more particularly the Cteno'ides and the 

 Cyclo'ides, and a very small number of species of the two pre- 

 ceding orders, which disappear insensibly, and of which the ana- 

 logous living species are considerably modified. As we do not 



