CHAPTER II 



THE STURGEON 



The class Pisces : the subclass Chondrostei — palaeozoic 

 Chondrosteans — the Paddle-fishes. The Sturgeon family : the 

 Sturgeon described — variation in number of scutes — only one 

 British species — distribution — size — food and habits — only 

 stragglers in our rivers — commercial importance — names 



WITH the exception of the Lampreys all the 

 freshwater fishes of the British Isles belong 

 to the class Pisces. In this class the body is usually 

 covered with scales, which in the more generalized 

 types have the form of juxtaposed rhombic bony 

 plates, but in the more specialized ones are thin, 

 rounded, and imbricated. Median and paired fins 

 are present ; they are supported basally by an 

 internal skeleton, and are also provided on each side 

 with a series of dermal rays. The endoskeleton may 

 be cartilaginous or bony, but there are always a 

 number of external or membrane bones ; the mouth 

 is bordered by bony jaws ; the pectoral arch is usually 

 connected with the skull by a series of bones. The 

 gill-sacs of the Lampreys are represented by clefts 

 leading from the pharynx into the branchial chamber, 

 which opens behind to the exterior, and is covered by 

 the opercular membrane, supported by the opercular 

 bones and branchiostegal rays ; the interbranchial 

 septa, or walls of the clefts, are so reduced that the 



