236 



On Oysters and Oyster-spat. By G. W. Hart. 

 (Read August 27th, 1869.J 



If an oyster be opened (on the flat shell) in the month of April, 

 there will be found on the left side of the heart a swollen gland 

 extending downwards for a considerable distance. This gland is 

 at this period filled with spermatozoa of the usual tadpole shape, 

 and in immense numbers. About the middle of May they dis- 

 appear, and the all important question which awaits solution is 

 whether these spermatozoa are discharged into the sea for im- 

 pregnation of the ova of other oysters, or are passed simply into 

 the ovaries of the same animal. 



Dr. Kelaart adheres to the first view, and at present that is also 

 my opinion, and if it be the correct one, then the clustering 

 together of oysters into banks is at once a provision for this mutual 

 impregnation, and a consequence of the mode by which the young 

 are discharged. After the discharge of the spermatozoa, veins 

 begin to appear in the ovaries, which soon cover as with network, 

 the whole body of the oyster, producing an appearance never see^ 

 when the fish is simply fat. These veins become gradually 

 thickened and from being filamentous in form, become corrugated or 

 beaded, and still later they are seen to be convoluted. 



Up to this date the ova are attached, but now the entire mass 

 appears to be set free, and if the ovary be cut, the eggs are dis- 

 charged in a granular state, having in a mass the appearance of a 

 rich cream. As the more forward ova are pressed along this canal 

 they receive their cilia, and become capable of locomotion, if placed 

 in water; they have as yet no appearance of shell and retain their 

 granular form, and if injured by pressure each egg may be seen dis- 

 solving into its constituent atoms, which retain for some little while 

 an independent vitality, — no organ is yet apparent. 



When the most advanced have reached this stage they are passed 

 into the mantle and receive their jarotecting shell, which appears to 

 be deposited by the parent oyster from the mucous which is found 

 more abundantly in that organ at this season than at any other 

 time. The ova may now be fairly considered to have reached the 



