THE FISHERY. 499 



If all goes on well, in a few days two little black specks are visible, 

 which are the future eyes, and in due time the little fish breaks through 

 the tough membrane which has invested it. At that period each little 

 fish has a large bag attached to its stomach, which is called the umbilical 

 vesicle ; this is covered with bright blood-vessels, by which the material 

 contained in the bag, which is destined to nourish the young fish, is 

 gradually absorbed. 



During the period required for hatching the eggs they should be 

 examined at least twice a week, and every egg which turns opaque 

 should be removed, or it is apt to be covered with a fungus (see Fungi, 

 fig. 859). The time required for the development of the egg is six 

 weeks, but it varies a little with the temperature, which it is always 

 desirable to keep down. On a warm day hundreds of young trout 

 will break through their shells, when they drop through the apertures 

 between the glass rods to the bottom of the vessel. 



During the whole time of hatching the ova, they should be kept 

 nearly in the dark, for if exposed to the light the eggs become covered 

 with a confervoid growth, which destroys them. I did not succeed well 

 till I learnt this fact, but now there is no difficulty, and very little 

 trouble, in obtaining any number of young fish. In a large hatch of 

 ova there are always some double fish, or Siamese twins. These live till 

 they lose the umbilical vesicle, when they die. 



When the umbilical vesicle is absorbed, food must be taken by 

 the mouth, and really at this period there is practically considerable 

 difficulty, for they must be supplied with food, and that food must be 

 in motion. It is supposed that they live on the entomostraca : they 

 certainly do not live on the diatoms, as I have examined their stomachs 

 to ascertain the fact. Fine scraped meat may be given to them, or very 

 fine pounded liver, but I prefer at once to turn them loose. On every 

 fine day after they have been placed in our streams the little fish may 

 be seen in great activity, continually darting at something which no 

 doubt is food, but which is too small for the human eye to distin- 

 guish. I turn them into little streamlets which I clear of all living 

 things as far as possible, as a little trout is a dainty morsel, highly 



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