vi.] ON THE STUDY OF ZOOLOGY. 89 



If I had worked my way from a sponge instead of a 

 lobster, I should have found it associated, by like ties, with a 

 great number of other animals into the sub-kingdom 

 Protozoa ; if I had selected a fresh-water polype or a coral, 

 the members of what naturalists term the sub-kingdom 

 Ccelenterata would have grouped themselves around my type ; 

 had a snail been chosen, the inhabitants of all univalve and 

 bivalve, land and water, shells, the lamp shells, the squids, 

 and the sea-mat would have gradually linked themselves on 

 to it as members of the same sub-kingdom of Mollusca ; 

 and finally, starting from man, I should have been compelled 

 to admit first, the ape, the rat, the horse, the dog, into the 

 same class ; and then the bird, the crocodile, the turtle, the 

 frog, and the fish, into the same sub-kingdom of Vertebrata. 



And if I had followed out all these various lines of classifi 

 cation fully, I should discover in the end that there was no 

 animal, either recent or fossil, which did not at once fall into 

 one or other of these sub-kingdoms. In other words, every 

 animal is organized upon one or other of the five, or more, 

 plans, whose existence renders our classification possible. And 

 so definitely and precisely marked is the structure of each 

 animal, that, in the present state of our knowledge, there 

 is not the least evidence to prove that a form, in the 

 slightest degree transitional between any of the two groups 

 Vertebrata, Annulosa, Mollusca, and Ccelenterata, either exists, 

 or has existed, during that period of the earth s history which 

 is recorded by the geologist. Nevertheless, you must not for 

 a moment suppose, because no such transitional forms are 

 known, that the members of the sub-kingdoms are discon 

 nected from, or independent of, one another. On the contrary, 

 in their earliest condition they are all alike, and the prim 

 ordial germs of a man, a dog, a bird, a fish, a beetle, a snail, 

 and a polype are, in no essential structural respects, 

 distinguishable. 



In this broad sense, it may with truth be said, that all 

 living animals, and all those dead creations which geology 



