12b MEMOIR OF CUVIER. 



Btant relation connects all modifications of the organism witli one another; that 

 certain organs exert on the collective animal economy a more marked and 

 decisive influence, whence the law of their subordination ; that certain facts of 

 oi'g'anization necessarily involve the presence of each other, while there are such, 

 on the contrary, as are incompatible and exclusive, one of the other, whence the 

 law of their correlation or coexistence ; besides so many other laws, so many 

 other general relations, which have^ in the end, created and developed the 

 philosophic part of the science. 



Among so many discoveries, so many particular facts with which he has 

 enriched that science, I must necessarily confine myself to a citation of the most 

 prominent, and still the catalogue of even these will be far from complete. The 

 researches of Hunter and of Tenon had already afforded valuable contributions 

 to the theory of the development of the teeth ; it was Cuvicr who earned this theory 

 to a perfection beyond which there can be little to desire. Those little bones 

 which we call teeth appear at first glance to be very simple, and scarcely to 

 merit the attention of the observer. These little bodies, however, are very 

 complex ; the}' possess secretory organs, as their gerrn^ their proper membrane ; 

 secreted substances, such as their enamel, i\\G\r ivory ; and each of these sub- 

 stances appears in its turn, each at a fixed epoch. They spring up, are devel- 

 oped, push forth their roots, die, fall, and are replaced by others with admiral)lo 

 order and regularity. Nor is it less admirable, though under another point of 

 view, that all the circumstances of their organization and development are to- 

 day rigorously demonstrated. It was chiefly through a study of the teeth of 

 the elephant, where everything is seen on a large scale, that M. Cuvier succeeded 

 in establishing the precise epoch at which each part of the tooth is formed, and 

 by what mechanism it is formed ; how each of these parts, having performed its 

 function of productive organ, disappears; how the entire tooth disappears in its 

 turn to give place to another, whicli will also have its development, both in the 

 whole and in detail, its point of complete organization, and its decay and its falL 



Perrault, Herissant, Vicq-d'Azyr, had, before Cuvier, distinguished some points 

 in the structure of the vocal organs of birds ; he has made that structure known 

 in a general manner and by detailed comparisons. It was he also who first 

 placed in a clear light tlie singular arrangement of the organ of hearing, and 

 still more singular aiTangement of the nasal yo55« in the cetaceous tribes. 



Every one knows the marvellous metamorphosis experienced by the frog in 

 passing from the state of fcetus or tadpole to the adult state. It is known that 

 after having respired, in the first case, b}'^ giUs, like the fishes, it respires, in the 

 second, T)y lungs, like the terrestrial animals. M. Cuvier has taught us the 

 structure of the organs of respiration and of circulation in a species of reptiles, 

 which presents something still more curious. The frog is by turns a fish in its 

 first stage, and a reptile in its second. These new reptiles, still more singular, 

 such as the protcus, the axolofl, the siren, are all their life re})tiles and fish; 

 have all the time l)oth hranchice or gills and lungs, and can hence breathe alter- 

 nately in the air and in water. 



M. Cuvier again was the first to give a connected comparison of the brain in 

 the four classes of vertebrate animals; the first to point (nit the relations of the 

 development of that organ with the development of intelligence, a brant^h of 

 comparative anatomy which has since become so fruitful and extensive ; the first, 

 in fine, to deduce in a rigorous manner from the respective quantity of respira- 

 tion of these animals, not only the degree of their natural heat, but that of all 

 their other faculties, their force of movement, their subtility of perception, their 

 rapidity of digestion. 



But the most novel and brilliant application which he has made of compara- 

 tive anatomy, is that which relates to fossil hones. Every one now knows that 

 the globe which we inhabit presents, almost everywhere, irrefutable traces of 

 stupendous revolutions. The productions of the actual creation, of living natiu'e, 



