133 THE PLACOID BRAIN. 



"Water fishes, the bones are lighter, and retain more animal 

 matter, than in those which swim in the denser sea. And 

 in the dolphin, a warm-blooded marine animal, they differ 

 little in this respect from those of the sea-fish. " Such being 

 the fact, it is surely but fair to inquire of the author of the 

 " Vestiges," why he should determine the rank and standing 

 of the Delphinidce according to one set of principles, and the 

 rank and standing of the placoids according to another and 

 entirely different set ? If the Delphinidce are to be placed 

 high in the scale, notwithstanding the softness of their skele- 

 tons, simply because their brains are large, why are the pla- 

 coids to be placed low in the scale, notwithstanding the 

 largeness of their brains, simply because their skeletons are 

 soft ? It is not too much to demand that, on the principle 

 which he himself recognises as just, he should either degrade 

 the dolphin or elevate the placoid. For it is altogether inad- 

 missible that he should reason on one set of laws when the 

 exigencies of his hypothesis require that creatures with soft 

 skeletons should be raised in the scale, and on another and 

 entirely different set when its necessities demand that they 

 should be depressed. 



But do the placoids possess in reality a large development 

 of brain ? I have examined the brains of almost all the com- 

 mon fish of our coast, both osseous and cartilaginous, — not, 

 I fear, with the skill of a Tiedemann, but aU the more intel- 

 ligently in consequence of what Tiedemann had previously 

 done and written ; and so I can speak with some little con- 

 fidence on the subject, so far at least as my modicum of ex- 

 perience, thus acquired, extends. Of all the common fish 

 of the Scottish seas, the spotted or lesser dog-fish bears, in 

 proportion to its size, the largest brain ; the gray or picked 

 dog-fish ranks next in the degree of development ; the rays, 

 in their various species, follow after ; and the osseous fishes 

 compose at least the great body of the rear; while still 



