THE RISE AND PROGRESS OF PALEONTOLOGY. 169 



consciously, guided the researches of paleontologists ever since. Even 

 that feat of paleontology which has so powerfully impressed the popu- 

 lar imagination, the reconstruction of an extinct animal from a tooth 

 or a bone, is based upon the simplest imaginable application of the 

 logic of Steno. A moment's consideration will show, in fact, that 

 Steno's conclusion that the glossopetrae are sharks' teeth implies the 

 reconstruction of an animal from its tooth. It is equivalent to the 

 assertion that the animal of which the glossopetrae are relics, had the 

 form and organization of a shark ; that it had a skull, a vertebral col- 

 umn, and limbs similar to those which are characteristic of this group 

 of fishes ; that its heart, gills, and intestines presented the peculiarities 

 which those of all sharks exhibit ; nay, even that any hard parts which 

 its integument contained were of a totally different character from the 

 scales of ordinary fishes. These conclusions are as certain as any based 

 upon probable reasonings can be. And they are so, simply because a 

 very large experience justifies us in believing that teeth of this partic- 

 ular form and structure are invariably associated with the peculiar 

 organization of sharks, and are never found in connection with other 

 organisms. Why this should be we are not at present in a position 

 even to imagine ; we must take the fact as an empirical law of animal 

 morphology, the reason of which may possibly be one day found in 

 the history of the evolution of the shark tribe, but for which it is 

 hopeless to seek for an explanation in ordinary physiological reason- 

 ings. Every one practically acquainted with paleontology is aware 

 that it is not every tooth nor every bone which enables us to form 

 a judgment of the character of the animal to which it belonged, and 

 that it is possible to possess many teeth, and even a large portion of 

 the skeleton of an extinct animal, and yet be unable to reconstruct its 

 skull or its limbs. It is only when the tooth or bone presents peculiar- 

 ities which Ave know by previous experience to be characteristic of a 

 certain group that we can safely predict that the fossil belonged to an 

 animal of the same group. Any one who finds a cow's grinder may be 

 perfectly sure that it belonged to an animal which had two complete 

 toes on each foot, and ruminated ; any one who finds a horse's grinder 

 may be as sure that it had one complete toe on each foot and did not 

 ruminate ; but, if ruminants and horses were extinct animals of which 

 nothing but the grinders had ever been discovered, no amount of 

 physiological reasoning could have enabled us to reconstruct either 

 animal, still less to have divined the wide differences between the 

 two. Cuvier, in the " Discours sur les Revolutions de la Surface clu 

 Globe," strangely credits himself, and has ever since been credited by 

 others, with the invention of a new method of paleontological research. 

 But if you will turn to the " Recherches sur les Ossemens Fossiles," 

 and watch Cuvier, not speculating but working, you will find that his 

 method is neither more nor less than that of Steno. If he was able to 

 make his famous prophecy from the jaw which lay upon the surface 



