GADUS 79 



Characters of Gadus which show an advance over the con- 

 ditions in Scyllium : 



Bone ; 



New marginal skeleton to the jaws ; 



New elements added to the pectoral girdle ; 



Swim-bladder. 



Characters of Gadus which are secondary when compared 

 with other forms : 



Continuity of the gonads with their ducts ; 

 Loss of optic chiasma ; 

 Loss of clavicle ; 

 Loss of conus arteriosus ; 



Swim-bladder closed, and adapted to hydrostatic 

 function. 



Literature 



Goodrich, E. S. Vertebrata Craniata : Cyclostomes and Fishes. Black, 

 London, 1909. 



Parker, T.J. A Course of Instruction in Zootomy (Vertebrata) . Macmillan , 

 London, 1884. 



