240 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



There is evidently a time when the embryo is callable of living an in- 

 dependent life, and is liable to attach itself to any body which may resist 

 its course. But when does this time come 1 Is it when the embryo is 

 expelled from the valves of the mother oyster, or leaves them volun- 

 tarily? Or is it necessary that it should first be in the water some time 

 in order to undergo a change and reach a greater degree of complete- 

 ness"? How long does its roving or pelagic life last"? All answers to 

 these questions are thus far mere conjectures and suppositious, and the 

 few successful experiments which have been made prove nothing con- 

 clusively or even precisely. 



In this direction, however, our efforts should principally tend, for 

 it would not matter if the fecundation of the common oyster proved 

 impossible, as long as we could succeed in keeping the legions of em- 

 bryos which it produces, and cause them to attach themselves to col- 

 lectors in close waters.* 



Pakis, France, H'ovemher, 1883. 



EXPLANATION OF PLATES. 



Plate II. — SLowiiig iiietbod of working. 



III. — 1. Supply of water to move tlio hydraulic wheel. 



2. Water- w^hecl for operating x»ump. 



3. Pinup for rcncwiiig tlie sea-water. 



4. Distributing pipe leceiviug the sea-water raised by the xjump. 

 G. Boxes for iucubatiou, liatcliing, and fixation. 



G. Basins containing the mother oysters. 

 IV. —A. Slate fixed to the bottom and sides of the box. 



B. Shite fixed to the sides, and raised about one inch from the bottom ot 



the box. 



C. Sand preventing the escape of the embryos. 



D. Outflow. 



V. — 1. Dike of Aruiaillo. 



2. Bay of Arcachon. 



3. AiguiHon Point. 



4. Board ]talisadcs, willi holes. 

 .5. Sand for filtering the water. 



G. Reservoir containing the embryos. 



"The quantity of spawn which is lost is truly enormous. Let us take, for instance, 

 the basin of Arcachon, a portion of the coast when* the greatest quantity of si)awn 

 is gathered regularly, owing to Ihe character of this immense reservoir, to which the 

 sea has access only through a narrow entrance. It is estimated that there are in tliis 

 basin upwards of a thousand millions of adult oy.sters, each emitting from 800,000 to 

 1,500,000 embryos. The annual harvest of spawn is estimated at 1,200,000, that is, 

 nearly one embryo to an oystcir; the loss, therefore, is not less than a million to each 

 oyster. 



