154 Proceedings of the 



by distinguishing the following epochs of the science of zoo- 

 logy: In the first, man regarded animals merely as he was in- 

 duced to seek or avoid them ; in the second, he was led by curiosity 

 to examine their different forms, independently of their actual 

 utility ; in the third, he felt the necessity of characteristic signs and 

 marks of distinction. The fourth was occupied by the details of 

 nomenclature, description, and classification. In the fifth, zoology 

 attained the rank of a science, properly so called ; and the era of 

 philosophical inquiry into the natural relation between the various 

 classes commenced. During the sixth, the idea of a primitive iden- 

 tity of organization began to develope itself, though in a somewhat 

 vague and uncertain manner; and in the seventh, at which we are 

 now arrived, science is occupied in developing the external causes in 

 which originate the various modifications which that primitive iden- 

 tity of organization has undergone in various animals. He remarks, 

 that in order to appreciate the action of external circumstances upon 

 an organized being, it is not sufficient to consider that being in its 

 perfect state of developement, we must study it at different periods of 

 its life. Thus we could not find any good reason for the depressed 

 and semi-elliptical form of the head of the frog, if we confined our 

 inquiries to the full-grown animal; but in tracing its origin, we 

 find that the frog, in its tadpole state, partook of the organiza- 

 tion of fishes, that is to say, it breathed through the voluminous 

 gills placed under the back cranium. Now, the bones of the 

 auricular region are the parts covering the gills, so that their deve- 

 lopement must necessarily be in proportion to the volume of 

 those gills ; thus the disposition of the bones of the head of the 

 frog has relation to the aquatic respiration of the tadpole. M. St. 

 Hilaire then traces the changes of organization through the various 

 phenomena of the universe, showing how the organic developement of 

 animals may have been affected, at various periods of their existence, 

 by the external changes in the material world. He particularly dwells 

 on the changes which may have been produced in the organs of 

 respiration, and the organs dependent on them, by the changes 

 which have gradually taken place in the atmosphere and tempera- 

 ture since the primitive ages ; by which he endeavours to account for 

 the modifications which, from a comparison of fossil remains with 

 existing animals, appear to have taken place in various species of 

 the animal kingdom. It is certain, he says, that the atmosphere 

 is no longer what it was, either in its chemical or physical proper- 

 ties ; and as the atmosphere cannot be modified without the respira- 

 tion, and consequently the whole animal economy, being modified 

 also, it follows that the existing animals, though descending directly 

 by way of generation from the ante-diluvian animals, differ materially 

 from them in organization. Man undergoes a change something 

 similar; it often happens that, in consequence of a germ being placed 

 in circumstances different from those in which it ought naturally to 

 be placed, the being to which it gives birth does not resemble its 



