BULLETIN OF THE UNITED STATES FISH COMMISSION. 331 



methods to the eggs of the unisexual oysters would none the less be a 

 fruitful operation. We see what occurs under natural conditions. The 

 mother oyster discharges its eggs in considerable numbers. Bat how 

 many are there of those which in the immensity of the surrounding- 

 waters find favorable conditions for their life? The estimation of the 

 losses is difficult, but if we base our calculation upon the proportions 

 indicated above, we will find that of the twenty millions of eggs pro- 

 duced daring one season but two millions ever attain the condition of 

 mobile larva 1 . 



Once brought to this phase of transformation, how many attach 

 themselves to the collectors? There is little hope that more than a 

 tenth part escape the manifold dangers by which they are constantly 

 surrounded. In the closed claires it is otherwise. We at once guar- 

 antee the impregnation of all the fertilizable eggs, placed as they are 

 in forced contact with the fecundating element. There is thus sup- 

 pressed the prime cause of the destruction of germs, without doubt the 

 most important. We also escape a second and also serious cause of 

 mortality, in protecting the embryos in the, closed reservoirs, where, 

 sheltered from dangers of all kinds to which they are exposed without, 

 they pass undisturbedly through the period of their pelagic existence, 

 till the time when they find themselves in need of the collectors, which 

 they will readily find, and to which they will fix themselves. 



Figures will be more eloquent than many arguments; one hundred 

 fertilized eggs have produced eighty mobile larvae. This is the mean result 

 of our experience at Verdou. Considered in its industrial relations, 

 the system of capturing the fry in closed waters would be infinitely 

 more economical than the present system. 



The only collectors suitable for great depths are the tiles, which, on 

 account of their weight, oppose a resistance to the currents ; boards, 

 slates, and other light bodies have been successively abandoned. But 

 the tiles are raised with difficulty after they are disposed in nests on 

 the beds. They are put out only when the fry is abundant, or when it 

 is being discharged during certain tides and favorable times. 



Iu confined waters [claires] we could put down or remove the collec- 

 tors at any phase of the moon, no matter what might be the state of 

 the sea, without incurring the risk of breaking them. Nor would it be 

 necessary to fix them to the bottom. Moreover, we would not employ 

 tiles exclusively, for, while the tile is an excellent collector, it also has 

 its disadvantages, especially on the shores of the Gironde, where this 

 mode of rearing the oyster is not in favor. Since their great weight 

 renders their transportation costly, they remain in position only till the 

 spat may have reached the size necessary for detrocage [or detachment], 

 from which cause the growth of the spat is delayed for a year. 



Xot to neglect any of the aspects iu which ostraculture may perhaps 

 be viewed, permit us to spy that the following methods appear practi- 

 cable: Firstly, the introduction and acclimation iu our waters of uni- 



