36 SCIENCE SKETCHES. 



median in position. Pectoral fins inserted low. 

 Lateral line present. Outline of belly rounded. 

 Vertebrae in large number, usually about sixty. 



The stomach in all the Salmonida is siphonal, 

 and at the pylorus are many (15 to 200) com- 

 paratively large pyloric cceca. The air-bladder 

 is large. The eggs are usually much larger than 

 in fishes generally, and the ovaries are without 

 special duct, the ova falling into the cavity of the 

 abdomen before exclusion. The large size of the 

 eggs, their lack of adhesiveness, and the readi- 

 ness with which they may be impregnated, render 

 the Salmonidcz peculiarly adapted for artificial 

 culture. 



The Salmonidce are peculiar to the North Tem- 

 perate and Arctic regions, and within this range 

 they are almost equally abundant wherever suitable 

 waters occur. Some of the species, especially the 

 larger ones, are marine and anadromous, living and 

 growing in the sea, and ascending fresh waters to 

 spawn. Still others live in running brooks, en- 

 tering lakes or the sea when occasion serves, but 

 not habitually doing so. Still others are lake 

 fishes, approaching the shore or entering brooks 

 in the spawning season, at other times retiring to 

 waters of considerable depth. Some of them are 

 active, voracious, and gamy ; while others are com- 

 paratively defenceless, and will not take the hook. 

 They are divisible into eight easily recognized 

 genera, Coregonus, Plecoglossus, Brachymystax, 

 Stenodus, Thymallus, Oncorhynchus, Salmo, and 

 Salvelinus. These groups may be discussed in 

 order. 



