148 THE PLACOID BRAIN. 



stage of the experiment, and see whether he may not be ahle 

 still further to develope tlie reptilian tail so obtained into 

 that of the mammal, by burning. Let him spread it out on 

 a piece of iron hoop, and thrust it into the fire ; and then, 

 after exposure for some time to a red heat has consumed and 

 dissipated its merely cartilaginous portions, such as the neural 

 and hcemal processes, with the little pieces which form the 

 sides of the neural arch, and left only the whitened bodies 

 of the vertebi-se, let him say whether the bony portion which 

 remains does not present a more exact resemblance to the 

 mammiferous tail, — that of the dog, for example, — than any- 

 thing else he ever saw. The Lamarckians may well deem 

 it an unlucky circumstance, that one special portion of their 

 theory should demand the depreciation of the heterocercal 

 tail, seeing that it might be represented with excellent effect 

 in another, as not merely a connecting link in the upward 

 march of progression between the tail of the true fish and that 

 of the true reptile, but as actually containing in itself, — as the 

 caterpillar contains the future pupa and butterfly, — the ele- 

 ments of the reptilian and mammiferous taiL If there be 

 any virtue in analogy, the heterocercal tail is, I repeat, of a 

 decidedly higher type than the homocercal one. It furnishes 

 the first known example in the vertebrata of those coccygeal 

 vertebrae diminishing to a point, which characterize not only 

 all the higher reptiles, but also all the higher mammals, and 

 which we find represented by the Os coccygis in man himself 

 But to this special point I shall again refer. 



With regard to that rudimentary state of the occipital 

 framework of the placoids to which the author of the " Ves- 

 tiges" refers, it may be but necessary to say that, notwith- 

 standing the simplicity of their box-like skulls, they bear in 

 their character, as cases for the protection of the brain, at least 

 as close an analogy to the skulls of the higher animals as 

 those of the osseous fishes, which consist usually of the extra- 



