THE PLACOID BRAIN. 139 



farther behind there lags a hapless class, — the Suctorii, — one 

 of which, the glutinous hag, has scarce any brain, and one, 

 the Amphioxus or lancelet, wants brain altogether. I have 

 compared the brain of the spotted dog-fish with that of a 

 young alligator, and have found that in scarce any percep- 

 tible degree was it inferior in point of bulk, and very slightly 

 indeed in point of organization, to the brain of the reptile. 

 And the instincts of this placoid family, — one of the truest 

 existing representatives of the placoids of the Silurian sys- 

 tem* to which we can appeal, — correspond, we invariably 

 find, with their superior cerebral development. I have seen 

 the common dog-fish, Spinax Acanthias, hovering in packs 

 in the Moray Frith, some one or two fathoms away from the 

 side of the herring-boat, from which, when the fishermen 

 were engaged in hauling their nets, I have watched them, 

 and have admired the caution which, with all their ferocity 

 of disposition, they rarely failed to manifest ; — how they kept 

 aloof from the net, even more warily than the cetacea them- 

 selves, — though both dog-fish and cetacea are occasionally 

 entangled ; and how, when a few herrings were shaken loose 

 from the meshes, they at once darted upon them, exhibiting 

 for a moment, through the green depths, the pale gleam of 

 their abdomens, as they turned npon their sides to seize the 

 desired morsels, — a motion rendered necessary by the posi- 

 tion of the mouth in this family ; and how next, their object 

 accomplished, they fell back into their old position, and waited 

 on as before. And I have been assured by intelligent fisher- 

 men, that at the deep-sea white-fishing, in which baited hooks, 

 not nets, are employed, the degree of shrewd caution exer- 



* The Silurian placoids are most adequately represented by the CeS' 

 tracion of the southern hemisphere ; but I know not that of the peculiar 

 character and instincts of this interesting placoid, — the last of its race, — 

 there is anything known. For its form and general appearance aee fig. 

 55, page 151. 



