132 liIGH STANDING OF THE PLACOIDS. 



to influence Linnaeus ; and though he no doubt pressed his 

 peculiar views too far when he degraded the glutinous hag 

 into a worm, and elevated the sharks and rays into reptiles, 

 it is certainly worthy of remark, that, in the scheme of clas- 

 sification which is now regarded as the most natural, — that 

 of Professor Muller, modified by Professor Owen, — the ich- 

 thyic worms of the Swede are placed in the first and lowest 

 order of fishes, — the Dermopteri, — and the greater part of his 

 ichthyic reptiles, in the eleventh and highest, — the Plagios- 

 tomi. Cuvier yielded, as has been shown, to the idea of re- 

 semblance founded on the material of the ichthyic framework, 

 and so ranged his fishes into two parallel lines. Professor 

 Oken, after first enunciating as law that " the characteristic 

 organ of fishes is the osseous system," confessed the "great 

 difiiculty" which attaches to the question of skeletal "tex- 

 ture or substance," and finally gave up the distinction founded 

 on it as obstinately irreducible to the purposes of a natural 

 classification. " The cartilaginous fishes," he says, " appear 

 to belong to each other, and are also usually arranged together; 

 yet amongst them we find those species, such as the lampreys, 

 which obviously occupy the lowest grade of all fishes, while 

 the sharks and rays remind us of the Reptilia." And so, sink- 

 ing the consideration of texture altogether, he placed the fa- 

 mily of the lamprey, including the glutinous hag, at the bot- 

 tom of the scale, and the sharks and rays at the top. Agassiz's 

 system, peculiarly his own, has had the rare merit, as I have 

 shown, of furnishing a key to the history of the fish in its 

 several dynasties, which we may in vain seek in any other. 

 His divisions, — ^if, retaining his strongly-marked placoids and 

 ganoids as orders stamped in the mint of nature, we throw 

 his perhaps less obviously divisible ctenoids and cycloids into 

 one order, the corneous or horn-covered, — are scarcely less 

 representative of periods than those great classes of the ver- 

 tebrata, — mammals, birds, reptiles, and fishes, — which we find 



