106 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



about 1*022 to 1'024, and Dr. Bashford Dean and others 

 state as their opinion that a low specific gravity is neces- 

 sary for a good deposit of spat. I asked Mons. Daste his 

 opinion on this point. He has had great experience as a 

 practical ostreo-culturist and has moreover been in the 

 habit of taking temperatures and specific gravities. He 

 said that unusually low specific gravities (due to wet 

 weather) during the breeding season did harm at Arcachon, 

 while further north at the other end of the" bassin " they 

 did good and resulted in more abundant spat because of 

 differences in the local conditions. 



Therefore it can scarcely be predicted for any particular 

 place whether a high specific gravity of the sea water will 

 or will not be advantageous for oyster culture. On the 

 whole Mons. Daste thinks that Salter water is better for 

 breeding and for the growth of the shell (" coquillage ") 

 but that less salt water — some admixture of fresh from 

 springs or streams — is better for the growth of the animal 

 (the soft parts in contradistinction to the shell) when one 

 or two years old. Certainly the French wild oysters that 

 I came across attached to rocks at low tide on the shores 

 of the open sea, although their shells might be well grown, 

 had the animal meagre, stringy, and saltish to the taste 

 and wanted the fatness and flavour of those reared in 

 " claires." 



At Arcachon the young oysters are allowed to remain 

 on the tiles at least till October or early in winter, when 

 they are about the size of the finger-nail, say J to f inch 

 in diameter (see PI. II, fig. 1). Then the tiles are collected 

 and taken ashore and the process of " detroquage " or 

 separating the oysters from the tiles takes place. This is 

 effected very rapidly by a skilled hand, the little oyster 

 with the film of lime to which it is attached being flicked 

 off the tile rapidly by a square-ended knife. 



