FISHES OF LAKE SUPERIOR. 259 



reference to the identification of fossil remains. It is therefore plain 

 that comparative anatomy should be more extensively and intimately 

 combined with zoology than is generally the case. The classification 

 of the animal kingdom should no longer be based simply upon the 

 structure of the animals, but form and structure should everywhere 

 and always be considered in their intimate connections. 



I have already alluded to the narrow circumscription of the genus 

 Lepidosteus, within the limits of the temperate zone of North Amer- 

 ica. In like manner, also, the Marsupialia, for instance, are almost 

 wholly confined to New Holland, and the Edentata to .Brazil. All 

 this goes to show that there is an important connection between a 

 given country and its inhabitants, which rests with the primitive plan 

 of the creation. 



The limited existence of Lepidosteus in North America in the pre- 

 sent creation has, no doubt, reference to the fact that North America 

 was an extensive continent long before other parts of the globe had 

 undergone their most extensive physical changes. Or in other 

 words, that the present character of this continent has not been 

 much altered from what it was when the ancient representatives of 

 Lepidosteus lived ; while in other parts of the world, the physical 

 changes have been so extensive as to exclude such forms from 

 among the animals suited for them. 



We have therefore here a hint towards a more natural and deeper 

 understanding of the laws regulating the geographical distribution of 

 animals in general. 



There are animals and plants whose detailed history is, as it were, 

 at the same time, the history of that branch of science to which they 

 belong. This is particularly the case with those animals, which, 

 from particular circumstances, have thrown unusual light upon the 

 relations which exist between them and their allied types. There 

 are even a few such animals, the study of which has actually marked 

 the advance of science. I cannot notice on this occasion the gar- 

 pike without being strongly reminded how strikingly this has been 

 the fact with Lepidosteus. The first sight I had of a stuffed skin of 

 that fish in the Museum of Carlsruhe, when a medical student in the 

 University of Heidelberg, in 1826, convinced me that this genus stood 

 alone in the class of fishes ; and that we could not, by any possibility, 



