210 THE STUDY OF ZOOLOGY vn 



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 burjdng groimds of 

 past ages, numberless lobster-hke 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 estabhsh a 

 complete body of zoological morphology. 



Again, we investigated the distribution of our 

 type in space and in time, and, if the Hke had 

 been done with every animal, the sciences of geo- 



