76 THE NEW AKT OF BREEDING FISH. 



■with like success in application to species that re- 

 quire only a very short period for incubation; for 

 notwithstanding that in such circumstances, develop- 

 ment of the embryo may be repressed, it still is go- 

 ing on to a certain extent, and the eggs may be 

 hatched in the sand before arrival at their destina- 

 tion. With the eggs of salmon and trout this diffi- 

 culty need not exist, for the time of incubation ex- 

 tends to forty-five or fifty days at least, and is pro- 

 longed even to a hundred or a hundred and ten days 

 if the temperature of the water is very low ; but 

 with such as hatch eight or ten days after being 

 spawned the same results cannot be hoped for, nor 

 can such kinds of eggs be conveyed to great distances. 

 Ordinarily, we use advantageously aquatic plants 

 instead of sand : we choose among the plants found 

 in the waters where the fish are taken whose eggs are 

 to be transported, such as are softest and least liable 

 to become matted together. We place in the boxes 

 alternately as with the sand, layers of leaves and of 

 eggs. When the box is filled the lid is closed, and 

 the humidity retained by the leaves suffices to pre- 

 serve the eggs. For several years past, Messrs. Ber- 

 thot and Detzem have sent me from the banks of the 

 Rhine, and from the establishment at Himingen, a 

 great number of these boxes, and I have had by 

 these means often as many as 10,000 eggs at a time 

 on the hurdles of my hatching apparatus at the Col- 

 lege of France, almost all of which have been hatched. 

 Recourse may be had to either of the processes I 



