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EXPLANATIONS 



of them belong to fan. {lies now living in our seas." He 

 instances a cestraceon — a high kind of placoid — recently 

 found in the Wenlock limestone, a low portion of the 

 Upper Silurians, and therefore near the beginning of fish 

 Some of the ganoids, also, of the Old Red Sandstone 

 make an approach to a higher class — reptilia. Besides 

 the usual row of fish- teeth, they have an inner range, in 

 which we see the form of those organs among the sauria. 

 It appears, in short, according to this writer, that the fur- 

 ther back we go among the fishes, we find them possessed 

 of the higher characters. Of the real character of all this 

 hardy assertion I shall enable the reader to judge. The 

 fishes of this early age, and of all other ages previous to 

 the chalk, are for the most part cartilaginous. The car- 

 tilaginous fishes — Chondropterigii of Cuvier — are placed 

 by that naturalist as a second series in his descending 

 scale ; being, however, he says, " in some measure par- 

 allel to the first" How far this is different from their 

 being the highest types of the fish class, need not De 

 largely insisted on. Linnaeus, again, was so impressed by 

 the low characters of many of this order, that he actually 

 ranked them with the worms.* Some of the cartilaginous 

 fishes, nevertheless, have certain peculiar features of or- 

 ganization, chiefly connected with reproduction, in which 

 they excel other fish ; but such features are partly par- 

 taken of by families in inferior sub-kingdoms, showing 

 that they cannot truly be regarded as marks of grade in 

 their own class. When we look to the great fundamental 

 characters, particularly to the framework for the attach- 

 ment of the muscles. w T hat do we find ? — why, that of 

 these placoids — " the highest types ot their class ! " — it 

 is barely possible to establish their being vertebrata at all, 

 the back-bone having generally been too slight for preser- 

 vation, although the vertebral columns of later fossil- 

 fishes are as entire as those of any other animals. In 

 many of them traces can be observed of the muscles hav- 

 ing been attached to the external plates, strikingly indi- 

 cating their low grade as vertebrate animals. The Edin- 

 burgh reviewer's "highest types of their class" are, in 

 reality, a separate series of that class — generally inferior, 



* Dr. Fletcher places the Chondropterigii lowest in a seal* 

 which takes as its criterion " an increase in the number and extent 

 of the manifestations of life, or of the relations which an organ 

 wed buing bears to the external world." 



