CLASS OF FISHES, 389 



into smolts, that is, they lose most of their generic characters, 

 and becoming covered with silvery scales, descend the fresh- 

 water streams to the ocean. It has been proved, experimentally, 

 that these smolts, which measure when they leave the pond for 

 the ocean only four or five inches, return to the rivers, in five or 

 six weeks, well grown fishes of five or even six pounds weight. 

 Such is the effect of their residence in the sea even for a few 

 weeks. But what is remarkable is that all the fry do not leave 

 the pond at the same time, though of the same size and age. A 

 full half remain, from causes unknown, and only descend to the 

 sea the following year. The cause of these anomalies, and even 

 the residence of the fry for a year in the fresh- water ponds, I am 

 inclined to ascribe to their being placed in an unnatural position ; 

 confined and cribbed, and so stunted in their growth and develop- 

 ment. Thus certain interesting questions in the history of the 

 salmon still remain unsolved : the first of these is the period 

 passed in the running stream, its natural habitat for the time 

 from the moment when it passes through the gravel (in April) to 

 its descent to the ocean as asmolt : experiments made in artificial 

 ponds cannot decide a question of this kind. Second, when young 

 salmon are detained in ponds, a certain number only leave the 

 ponds after the second year of their residence in such waters ; 

 what becomes of these ? Third, what is the true nature of the 

 smolt, first called par, which frequents at all seasons the rivers 

 from near their sources to the estuaries in which they terminate ; 

 which so closely resembles the young of the salmon before it 

 assumes its silvery scales ; which is male and female in nearly 

 equal numbers, but in which the ova of the female are never 

 developed, whilst the milt of the male is found developed nearly 

 at every season of the year. R. K.] 



493. The habits of fishes do not offer many curious 

 particulars ; nevertheless, reflecting on their importance but 

 a few years ago in the history of the maritime nations of 

 Europe, and that in France there are from thirty to forty 

 thousand seafaring men still engaged in this branch of in- 

 dustry, extending their voyages to the coasts of Iceland and 

 Newfoundland in quest of the cod (Fig. 398), a large and 

 excellent fish abounding on these coasts, though not on ours, 

 the subject cannot be said to be without interest. 



494. Classification. Fishes form one of the most 

 numerous classes of the animal kingdom, and are usually 

 divided into two series, according to the nature of their 

 skeleton. 



The group or sub-class of osseous fishes is by far the most 

 numerous in genera and species. It is composed of all the 



