360 ON THE STUDY OF ZOOLOGY 



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 disconnected from, or independent of, 

 one another. On the contrary, in their earliest condition 

 they are all alike, and the primordial 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 

 reveals, are bound together by an all-pervading unity of 

 organization, of the same character, though not equal in 

 degree, to that which enables us to discern one and the same 

 plan amidst the twenty different segments of a lobster's 

 body. Truly it has been said, that to a clear eye the smallest 

 fact is a window through which the Infinite may be seen. 



Turning from these purely morphological considerations, 

 tet us now examine into the manner in which the attentive 

 study of the lobster impels us into other lines of research. 



Lobsters are found in all the European seas ; but on the 

 opposite shores of the Atlantic and in the seas of the 

 southern hemisphere they do not exist. They are, however, 

 represented in these regions by very closely allied, but 

 distinct forms the Homarus Americanus and the Homams 

 Capensis : so that we may say that the European has one 

 species of Homarus ; the American, another ; the African, 



