hand, or the collar-bone and blade-bone, or the 

 bones of the pelvis, on the other, is very obscure 

 in man, but very obvious in many of the lower 

 animals, as fishes and birds ; and, that between 

 the lower jaw and legs, which in man is ex- 

 ceedingly difficult to be detected, is perfectly ob- 

 vious in some invertebral animals, as the cray- 

 fish. Let us pause, then, before we deny that the 

 reputed analogies, which have been pointed out 

 between the several organs of the human body, 

 have any existence ; or, that the science which 

 investigates the laws which regulate these analo- 

 gies, is susceptible of any useful application. 



But such analogy such unity of organiza- 

 tion is much more striking, when we come to 

 compare certain organs of one animal with the 

 corresponding organs of another ; the conviction 

 being now almost forced upon us, that the vis 

 plastica really operates according to certain fixed 

 rules, from which it does not, in any case, recede. 

 One of the best examples of this kind of analogy 

 is that which subsists in a certain class of organs, 

 as found in two individuals of the same species, 

 but of different sexes an analogy which seems to 

 have been noticed first by Aristotle, and to have 

 impressed upon him the first idea, which was 

 ever entertained, of a general unity of organic 

 structure. I am unwilling to prosecute this 

 subject at present ; but I may be permitted to 

 observe, before leaving it, that, in the embryo of 

 most animals, the organs above alluded to are 

 almost entirely the same, whichever is to be its 



