EMBRYO OYSTERS. 247 



increase the number of the movable pieces waiting the 

 gathering season. 



The oysters generally spawn from June to the end of 

 September, but do not leave their om, like many other 

 marine creatures. They incubate them in the folds of 

 their coverlet (mantle) and among the laminae of the 

 branchiae (lungs). There they remain surrounded by 

 mucous matter necessary to their being developed, and 

 within which they pass through the embryo state. The 

 mass of ova, in consistence and colour, resembles thick 

 cream, and breeding oysters are therefore termed milky. 

 The pale tint which first characterises them, gradually, 

 in the process of development, changes to bright yellow, 

 then to a darker yellow, and ends in a greyish-brown 

 or a very marked greyish-violet. The whole mass, 

 which meanwhile is losing its fluidity, probably by ab- 

 sorption of the mucous matter enveloping the ova, is 

 then like a piece of compact mud. This indicates the 

 near termination of the development, and the expulsion 

 of the embryos, and their independent existence ; for 

 by this time they can live well enough without the pro- 

 tection of the maternal organs. On leaving the mother 

 they are furnished with a swimming apparatus (its 

 singular nature has been discovered and described by 

 M. le Docteur Davaine), enabling them to move to a 

 distance in eearch of solid bodies to which they may 

 attach themselves. 



The oyster produces not less than from one to two 

 millions of young, so that the animated matter escaping 

 from all the adults in a breeding bank is like a thick 

 mist dispersing from the central spot from which it 

 emanates, and so scattered by the waves that only an 

 imperceptible portion remains near the parent stock. 

 All the rest is dissipated ; and if these myriads of wan- 

 dering animalcules, borne about by the waves, do not 

 meet with solid bodies to which they may attach them- 

 selves, their destruction is certain ; for those which do 

 not become the prey of the lower creatures living on 



