vi.] ON THE STUDY OF ZOOLOGY. 103 



the relations which these have to worms and other lower 

 animals, are expressed by combining the whole vast 

 aggregate into the sub-kingdom of Annulosa. 



DO <^ O 



11' 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- 

 kin odom Protoxoa; if I had selected a fresh-water 

 polype or a coral, the members of what naturalists 

 term the sub-kingdom Ccclenterata 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 

 classification 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 pre- 

 cisely 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 Cwlenterata, 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 



