508 PISCES SUB- CLASS III. TELEOSTOML 



stricted to the cooler portions of the Northern Hemisphere, although one 

 genus is found in the fresh waters of New Zealand. Whereas some kinds 

 spend the whole of their time in fresh water lakes or rivers, others descend 

 periodically to the sea or, as it is perhaps more correct to say, ascend rivers 

 from the sea for the purpose of spawning. Certain kinds are, however, per- 

 manently marine, most of these being deep-water fishes, although the mem- 

 bers of two genera are pelagic. On account of the large size of many of the 

 species, coupled with the superlatively excellent quality of their flesh, the 

 Salmonidm are commercially one of the most valuable families of fishes. It 

 appears that the "salmon-colour" characterising the flesh of some of the 

 species is due to the pigment derived from the crustaceans on which they 

 feed ; the action of the gastric juice turning such pigment red in the same 

 manner as boiling. Volumes have been written on the life-history of the 

 Salmonidce, and the question as to the number of species of fresh-water trout 

 and charr ; and many pages of this work would be necessary to give even a 

 full outline of the subject. As it is, little more than a bare mention of the 

 leading genera and species can be attempted. It should, however, be men- 

 tioned that whereas the adults are usually silvery, or spotted with black and 

 red, the immature fish pass through a stage the "parr" when they are 

 marked by dark transverse bars. In certain fresh-water kinds these imma- 

 ture markings may, however, be retained individually during the whole of 

 life. There are also sexual or seasonal differences in the adult fish ; as 



exemplified by the hooked lower 

 jaw of the male salmon in the 

 spawning season. The genus 

 Salmo, which includes the com- 

 mon salmon (S. salmo), and the 

 various species or varieties of trout 

 and charr, has the dorsal fin 

 Fig. 31. THE SALMON. situated nearly or immediately 



above the pelvic pair, the scales 



small, and well-developed teeth in the jaws, and likewise on the vomerine 

 and palatine bones and tongue ; while the anal fin never includes more than 

 fourteen rays, and the intestine is furnished with a large number of small 

 blind appendages or caeca. Moreover, the mouth is so deeply cleft, that its 

 opening extends at least as far back as the eye. Southwards, the range of 

 this large genus does not extend beyond the Atlas and Hindu Kush in the 

 Eastern Hemisphere, or the rivers flowing into the head of the Gulf of 

 California in the Western. In the various kinds of true salmon and trout the 

 whole length of the bone known as the vomer carries teeth during some 

 period of life. On the other hand, in the mostly smaller and more brilliantly- 

 coloured charr the vomerine teeth are restricted to the head of that bone. 

 The largest member of the charr group is the Danubian hucho (8. hucho), 

 which rivals the salmon in size. The migratory species, which periodically 

 ascend the rivers of North America and Asia flowing into the Pacific in in- 

 credible numbers, form the genus Onchorhynchus, distinguished by the 

 possession of more than fourteen rays in the anal fin. A third genus 

 (Osmerus) contains the three species of smelt, and is to some extent inter- 

 mediate between Salmo and Onchorhynchus on the one hand, and Coregomts 

 on the other. They are, however, peculiar, on account of the small size and 

 number of the csecal appendages to the intestine, while their eggs are rela- 

 tively small. As examples of the large and mostly fresh-water genus Core- 



