vi.] ON Til E STUDY OF ZOOLOGY. 105 



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 

 distribution 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. Morpho- 

 logy and distribution 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 remarkably. 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 climb- 

 ing actively the submerged rocks, among which it delights 

 to live, by means of its strong legs ; or swimming by 

 powerful strokes of its great tail, the appendages of 

 whose sixth joint are spread out into a broad fan -like 



