502 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



still in motiou wlien the process of fecundation goes on, and should be 

 able to take their course toward the opening of the channel and pene- 

 trate into the interior of the egg. We have seen that the movement of 

 the spermatozoids cease rery soon after diluting the milt with water ; 

 it is, therefore, highly important, for a successful fecundation, to dilute 

 the milt and impregnate the spawn with the mixture as rapidly as pos- 

 sible. The inner bladder of the egg contains albumen and yolk; this 

 latter is at first spread throughout the whole bladder, but after fecun- 

 dation it all collects on one point and forms a separate yolk, (vitellus.) 

 Then the yolk divides into two hemispheres, which again are divided; 

 then the vitellus occupies two-thirds of the bladder. Finally it is pos- 

 sible to distinguish the head, the vertebral column, and the tail of the 

 embryo ; and^about a month before being hatched the eyes can be dis- 

 tinguished in the shape of two black spots. In the lavaret they can 

 already be seen in January. 



The skin of the egg is soft before being fecundated, but after fecunda- 

 tion it becomes thicker and so hard that it is almost impossible to crush 

 the egg between the lingers. Toward the end of the development of 

 the egg, the skin secretes a substance destined for forming the hard 

 portions of the embryo, and then it becomes transparent, tine, like the 

 web of a spider, and so delicate, that at the least outside pressure it 

 tears on all sides. 



After the fish has come out, it carries with it the umbilical bag con- 

 tainiug a supply of nutritive substance, which is absorbed by means of 

 blood-vessels spreading all through the bag. After all has been absorbed, 

 the young being has the perfect form of a fish, and is called fry, (" alevin ;") 

 it now requires outside food. 



The hatching of fish is not done all at once, but gradually, under the 

 influence of certain external causes, such as the temperature of the water, 

 the quantity of oxygen contained in it, &c. It is necessary to watch 

 the temperature and purity of the water very carefully. Dust floating 

 in the air over the water, and various impurities which fall in the water 

 and mix at the bottom of the basins with innumerable microscopic 

 pieces of vegetable fiber, form tufts, in which, if the temperature of the 

 water is higher than 50O-Fahr., myriads of infusoria develop. These 

 tufts get iuto the mouths of the young fish, and, being ejected together 

 with the water, obstruct the gills and produce suffocation. 



After having absorbed the umbilical bag, the fish seeks other food. 

 The possibility of satisfying this want during the first time has a 

 decided influence on the further development. The young fish shows 

 by its first movements an innate tendency to seize food, just as mam- 

 malia immediately after their birth instinctively seek the breast which 

 is to give them food. As regards the most suitable food for young fish, 

 the trout and the salmon family chiefly feed on animate matter, e.g., on 

 the spawn or the young of the Cyprinm alburnus, Cuv.; on the Cyprinus 

 leucisciis, Cuv., {or Aspius alburmis, Agass.;) or on fish of the species 



