20 FISHES. 



amined throughout the whole class, and their relative import- 

 ance has been duly weighed and understood. Though 

 Linnaeus had formed a category of " Amphibia nantes " for 

 fishes with a cartilaginous skeleton, which should coincide 

 with Cuvier's " Poissons Cartilagineux,'' he had failed to 

 understand the very nature of cartilage, apparently comprising 

 by this term any skeletal framework of less firmity than ordi- 

 nary bone. Hence he considered Zophius, Gyclopterus, Syng- 

 natlius to be cartilaginous fishes. Adopting the position and 

 development of the ventral fins as a highly important charac- 

 ter, he was obliged to associate fishes with rudimentary and 

 inconspicuous ventral fins, like Trichiurus, Xiphias, etc., with 

 the true Eels. The important category of a " family " appears 

 now in Cuvier's system fuUy established as that intermediate 

 between genus and order. Important changes in Cuvier's 

 system have been made and proposed by his successors, but 

 in the main it is still that of the present day. 



Cuvier had extended his researches beyond the living 

 forms, into the field of palaeontology ; he was the first to 

 observe the close resemblance of the scales of the fossil 

 Palceoniscus to those of the living Polypterus and Zepidosteus, 

 the prolongation and identity of structure of the upper caudal 

 lobe in Palceoniscus and the Sturgeons, the presence of peculiar 

 " fulcra " on the anterior margin of the dorsal fin in Palceoniscus 

 and Zepidosteus: inferring from these facts that that fossil 

 genus was allied either to the Sturgeons or to Zepidosteus. 

 But it did not occur to him that there was a close relationship 

 between those recent fishes. Zepidosteus and, with it, the fossil 

 genus remained in his system a member of the order of 

 Malacopterygii abdominales. 



It was left to L. Agassiz (born 1807, died 1873) to point 

 out the importance of the character of the structure of the 

 scales, and to open a path towards the knowledge of a whole 

 new sub-class of fishes, the Ganoidei. 



