THE NEW ART OF BREEDING FISH. 15 



It is necessary to take all these precautions ia or- 

 der that the water flowing through the gravel may be 

 purged of its impurities before it enters the box, and 

 not deposit mud and slime upon the eggs and retard 

 or prevent altogether the hatching ; as Gehin and 

 Eemy observed was the case when such precautionary 

 measures were omitted. 



The box so placed is left for a month or two. Mr. 

 Gehen could not determine the exact time of the 

 process of incubation, as it varied with the quality of 

 the water. This question is now occupying the at- 

 tention of scientific men, and from their researches 

 we shall have the exact results. 



In place of using a box, a hole may be dug in the 

 gravel, and the eggs may be deposited in it and cov- 

 ered over with pebbles in the manner practised by the 

 fish. But the progress of the incubation cannot 

 then be as accurately watched as with a box, which 

 can be opened and closed at pleasure. 



Mr: Gehin observed these phenomena of the 

 hatching : the tail comes first from the egg, and the 

 pieces of the fine skin or shell torn by it, form the two 

 hinder fins. The head next appears at the other end, 

 and the torn shell there forms the forward fins. The 

 lower part of the egg forms the belly, and the upper 

 part next is broken, and the back appears. The 

 shell or skin which enveloped the embryo is not de- 

 tached from the newly-born fish, but becomes a part 

 of and is absorbed by it. 



