ON THE STUDY OF ZOOLOGY 361 



another ; and thus the remarkable facts of geographical 

 distribution begin to dawn upon us. 



Again, if we examine the contents of the earth's crust, 

 we shall find in the latter of those deposits, which have 

 served as the great burying grounds of past ages, number- 

 less lobster-like animals, but none so similar to our living 

 lobster as to make zoologists sure that they belonged even to 

 the same genus. If we go still further back in time, we 

 discover, in the oldest rocks of all, the remains of animals, 

 constructed on the same general plan as the lobster, and 

 belonging to the same great group of Crustacea ; but for 

 the most part totally different from the lobster, and indeed 

 from any other living form of crustacean ; and thus we 

 gain a notion of that successive change of the animal 

 population of the globe, in past ages, which is the most 

 striking fact revealed by geology. 



Consider, now, where our inquiries have led us. We 

 studied our type morphologically, when we determined its 

 anatomy and its development, and when comparing it, in 

 these respects, with other animals, we made out its place 

 in a system of classification. If we were to examine every 

 animal in a similar manner, we should establish a complete 

 body of zoological morphology. 



Again, we investigated the distribution of our type in 

 space and in time, and, if the like had been done with every 

 animal, the sciences of geographical and geological dis- 

 tribution would have attained their limit. 



But you will observe one remarkable circumstance, that, 

 up to this point, the question of the life of these organisms 

 has not come under consideration. Morphology and dis- 

 tribution might be studied almost as well, if animals and 

 plants were a peculiar kind of crystals, and possessed none 

 of those functions which distinguish living beings so re- 

 markably. But the facts of morphology and distribution 

 have to be accounted for, and the science, whose aim it is 

 to account for them, is Physiology. 



Let us return to our lobster once more. If we watched 

 the creature in its native element, we should see it climbing 

 actively the submerged rocks, among which it delights to 

 live, by means of its strong legs ; or swimming by power- 

 ful strokes of its great tail, the appendages of whose sixth 

 joint are spread out into a broad fan-like propeller : seize 

 it, and it will show you that its great claws are no mean 

 weapons of offence ; suspend a piece of carrion among its 



