GREAT BRITAIN. 127 



Diseases. The members of the cod family appear to 

 be very susceptible to disease, especially of the vertebral 

 column, which may become shortened, and has been com- 

 pared by Dr. Dyce to a form of rickets, occasioning angular 

 or lateral curvature. This may cause a diminution in the 

 extent of surface covered by the dorsal or anal fins, which 

 from this, or other causes, vary greatly in the number of 

 their rays. Sometimes it gives the fish a hunch-backed 



ippearance, or the proportionate length of the head to that 



>f the body becomes far greater than is normally the case. 



Uindness is not rare among these fishes, especially when in 

 ifinement. The presence of parasites may not only alter 

 le colours of the fish as shown by its being of an un- 



laturally light tint, but also by the infected spots turning 



lack, as seen in the speckled cod. 



GENUS i. The Cod (Gadus). 



The reason why these fishes were termed A sinus by the 

 ancients has by some been considered to have reference to 

 their colour; while others believe it to be due to their 

 having been carried to market on the backs of asses. 

 Yarrell, however, advanced another suggestion, that the 

 term was originally intended for the haddock, in which (he 

 says) the shoulder blotch frequently extends over the back, 

 uniting with that on the opposite side, and thus reminding 

 the observer of the dark stripe over the withers of an ass. 

 A slight objection might be raised as to whether it can be 

 considered probable that the Greeks and Latins conferred 

 this term on a species which does not exist in their seas. 

 The name has also been supposed to refer to the hake. 



This genus was subdivided by Cuvier into (i) those in 

 which three dorsal fins and a submandibular barbel were 



i 



