226 



EXPLANATIONS 



of them belong to fan dies now living in our seas." Ha 

 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, w T as 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 of 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 re.ktions which an )rgan 

 ned bting bears to the external world." 



