84 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 
Mackerel.—The mackerel, too, he found to have the same characteristic, 
-the eggs of both species being found far out at sea. In both cases the 
egg was provided with a small globule of oil, apparently for the express 
purpose of facilitating its suspension in the water, and which was con- 
tained in the abdominal sack of the young fish in hatching, and con- 
stituted a large part of its embryonic nutriment. 
Plaice—The eggs of the plaice, too, one of the principal flat-fish of 
Europe, were found floating freely in the sea, and the inference was 
drawn that most of the flat-fish family, including the turbot, sole, &e., 
possessed the same characteristics. An analogy in the habits and phys- 
iological condition of other species of the cod family, such as the had- 
dock, the pollock, and the hake, also induced Sars to include them in 
the same category. 
As a general rule, the eggs of fish that float freely in the sea are 
single, and belong to the so-called dry eggs, or lack the glutinous en- 
velope which is found in the case of the herring and some less impor- 
tant fish, which causes them to adhere to each other in masses and to 
any other object with which they may come in contact. The herring is 
almost the only sea fish of economical importance that exhibits the last 
mentioned characteristic. (Deep Sea Fishing, p. 42.) 
Many forms of animal life, including fishes of the various Antennarius, 
Chironectes, &c., live habitually in mid-ocean, especially among the 
masses of floating sea-weeds, of which some species actually make nests 
in which their eggs are introduced. 
The rate of growth of the young fish varies with the group. In Crys- 
tallagobius, according to Collett, and perhaps in other forms, the capac- 
ity of reproduction is developed in a year’s time. For the most part, 
however, it is thought that the ordinary fishes require a period of three 
or four years before they are able to propagate their kind. It is likely 
that the sharks require a still greater allowance, although nothing defi- 
pite is known on this subject. 
The actual rate of growth of the individual varies with the species, 
-and probably to a certain extent with the individual, and the average 
at maturity varies very much with different so-called schools. Thus 
among the codfish, a school of mature fish coming in to the coast of 
New Jersey and elsewhere on the south side of New England, may aver- 
age not more than 5 to 10 pounds, while another school, which visits 
Cape Ann for the same purpose, averages a much greater weight, indi- 
viduals of even 100 pounds not being extremely rare. The same dif- 
ference in the size of cod occurs elsewhere, as also in that of other 
kinds of fish. What causes this difference it is, of course, impossible 
to say. j 
Many fishes experience curious changes of shape and color during the 
breeding season. These alterations are very much marked in the sal- 
mon, the male of which develops a lengthened, hooked jaw, in which 
formidable teeth make their appearance, A common alteration consists 
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