532 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



millions of fully-developed eggs, -while Lotella and Halargyreus have 

 only a fevr thousand. 



The cod family has a remarkable tendency to variation, as is most 

 strikingly apparent in the difficulty of defining genera and species 5 the 

 species show many varieties {Oadiis morrhua, near Great Britain, has 

 two, a light-colored one in the north and a dark one in the south), 

 the genera, numerous species, &c., throughout the whole family. The 

 caudal or tail fin is never placed at the end of the terminal vertebra, 

 but has its lower portion slightly in front of it, and even unites some- 

 times with the anal fin ; the scales are frequently ctenoidal,* and thus 

 also similar to those of the fishes of former ages. Sometimes the eyes are 

 very large, which is usually considered as peculiar to the more recent 

 forms of fishes, as the number of barbels also is most probably an indi- 

 cation of the stage of development, increasing or diminishing with the 

 antiquity of the fish. The head is often comparatively small, as with 

 Brosm'ms vulgaris; often large, as with Gadus macroce])lialits, and some- 

 times the lower jaw is elongated and hook-shaped — a mark of antiquity, 

 according to the analogy of the salmon. I therefore conclude that the 

 family is still in the process of development, namely, from fresh-water 

 into salt-water fish. 1 do not assert, however, that the saltness of the 

 ocean is greater at present than in former ages, but I wish to state the fact 

 that the codfish, Gadidce, also at previous periods lived in regions of the 

 sea where the water was but slightly salt; for in the present time, too, 

 they live moie particularly in fresh and brackish water, or in sea-water 

 of not more than 2 to 3 per cent, of salt.t 



The Lota vulgaris is a true fresh-water fish in the lakes and rivers of 

 Central, Northern, and Eastern Europe, Northern Asia, and northern 

 North America, and yet, according to Pallas, it also occurs in the Arctic 

 Ocean, on the coast of Siberia, as far as Indigirka, and according to 

 Eathk6 in the Black Sea, and according to Yarrell in the Frith of Forth. 

 Others live in the open ocean, but their old habit drives them into the 

 rivers again. Thus the cod migrates up the Tweed. The Gadus macro- 

 eephalus, according to Pallas, frequents the ocean around Kamtschatka 

 and America, but ascends the rivers in May and returns to the ocean in 

 August and September, after remaining about four months in fresh 

 water. 



They all live in regions of the sea where the water contains but 

 little salt, especially at the mouths of rivers, fresh-water basins, ports, 

 &c. They require a temperature of the water of from 39o to 440; the 

 Lota vulgaris can endure a somewhat lower temperature, and the south- 

 ern forms, Physiculus and Uraleptus, will bear a somewhat higher ; thus 

 the family belongs to the temperate zone, and its occurrence indicates 

 unmistakably a medium temperature, even where such might not be 



* The gadoids, as now limited, all have cycloid scales. — T. H. B. 



t Microgadus tomcodus has been transferred suddenly from salt water to a fresh-water 

 aquarium and kept alive for months. — T. H. B. 



