1 68 



A HISTORY OF FISHES 



of this difference in flavour is interesting. In the Plaice, as in 

 most other fishes, the chemical substance is present in the flesh 

 when the fish is ahve, but unless it is eaten soon after capture 

 this soon fades away and the flesh becomes comparatively 

 tasteless.^ In the Sole, on the other hand, the characteristic 

 flavour is only developed two or three days after death in 

 consequence of the formation of a chemical substance by the 

 process of decomposition : thus, it forms a tasty dish even when 

 brought long distances. 



After the muscles the ahmentary canal or food channel may 

 be considered, that lengthy tube which commences at the 

 mouth and ends at the vent or anus. The ahmentary system 



Srai'n 



\ Air-bladder 

 Testis 

 Intcitine 



Fig. 68. INTERNAL ORGANS. 



Dissection of a Perch {Percafluviatilis), showing the principal internal organs, X I. 



also includes the mouth, jaws, and teeth, which have been 

 already described, and such glands as the Hver, pancreas, and 

 spleen (Fig. 68). The ahmentary canal is found in its simplest 

 and most primitive condition in the Lampreys and Hag-fishes 

 (Cyclostomes), where it forms a straight tube running from 

 mouth to vent, with the different regions scarcely indicated, 

 but m the Selachians and in the vast majority of Bony Fishes 

 the pharynx is followed in succession by a gullet, a stomach, an 

 mtestme, and a rectum. Commencing with the mouth, it 

 may be noted that there is never a protrusible tongue in fishes, 

 this organ serving merely as an organ of taste instead of being 

 used to assist in the mastication of the food. Further, although 

 the mouth and intestine both pour out a more or less copious 

 supply of mucous to lubricate the food mass and assist its 



