28 THE POPULAR SCIENCE MONTHLY. 



nute opening through which a particle of the spawn — the soft roe — of 

 the male fish enters, and the egg is fertilized. From this moment the 

 young fish gradually develops, under the influence of the cold running 

 water. At the end of about thirty-five days — more or less, according 

 to the temperature, which should be about 40° — two little black specks 

 can be seen, as at Fig. 2, which are the eyes of the embryo fish ; the 

 vertebras may be discerned in the form of a faint red line, and a small 

 red globule, which shortly afterward appears, represents the vital or- 

 gans of the embryo fish. 



At the end of about 80 to 100 days from the deposition of the egg 

 the fish has so increased in size that it bursts the " shell " and makes 

 its debut in the form represented at Fig. 3. The sac or umbilical vesi- 



Fig. 3. 



Fish coming out of Egg. 



cle attached to the under part of the fish contains a secretion re- 

 sembling albumen, which affords nourishment to the infant fish for 

 the first six weeks or so of its existence. By that time it is quite 

 absorbed, and for the first time we see a perfect fish, Fig. 4, with 

 its fins, gills, and scales, which have hitherto been present, but im- 

 perceptible except under the microscope, fully formed : and now the 

 young salmon begins to feed. His growth is not very rapid for some 

 months, the lines a, b, c, representing the average length of a salmon at 

 two, three, and four months old. At two years old the fish is about 

 nine to twelve inches long. 



As soon as they are large enough and strong enough, the " smolts," 

 as they are now called, descend to the sea ; here they are lost sight 

 of until they return up the river as " grilse." The actual duration of 

 their stay in the sea is not yet known, from one to three years being 

 variously estimated as the probable length of time. The object of this 

 migration to the sea is to find the food which is necessary for the 

 secretion of the fat of the fish, who lives on the Infusoria, smaller 

 fish and crustaceans, and the spawn of sea-fish, which abound in our 

 seas. The length of their stay in salt-water is regulated, no doubt, 

 by various circumstances, and is not the same in every case. When 

 the salmon has laid up a sufficient supply of fat in its body and on 

 its pyloric appendages, which are a wonderful provision of Nature for 

 the secretion of an amount of fat sufficient to supply it during its so- 



