VERTEBKATA. 



257 



notoclioi'd is placed ; and the vertebrae of fishes are 

 therefore said to be biconcave or amphicselous. The 

 scales of the Teleostei are sometimes round at the edges 

 (cycloid), and sometimes fringed at the edges (ctenoid 

 or comb-like). The order is divided into a gi'eat 

 number of sub-orders, tribes, and families. The 

 PleuronedidcB, or Flat-fishes, which include the Sole 

 (fig. 94), Flounder, and Plaice, deserve a word of 

 notice because they are among the commonest fishes 



Fig. 93.— Scales of Fish: A, Cycloid j B, Ctenoid; C, Ganoid; B, Placoid. 



of our coast, and are at the same time very ex- 

 ceptional in their structure. They have become 

 curiously adapted to their habit of lying on the 

 sandy bottom of the sea, their bodies being both 

 twisted and flattened, apparently by constantly lying 

 on one side, so that the arrangement of the head 

 and bones is crooked with regard to the original 

 median plane of the body, and adapted to the new 

 median plane developed by the flattening process. 

 The result is, that both eyes are placed on one side 

 of the head. Flattened animals, as has already been 



