a. W. HART ON OYSTERS AND OYSTER-SPAT. 237 



embryo state, their colour is rapidly changing, the internal organs 

 become gradually developed, and the stomach and liver become 

 apparent as a dark spot, which causes the deeper tint of the mass 

 of embryoes. 



When warm weather sets in early in the spring, immense num- 

 bers of the young in this state are to be found in the sea, and not 

 unfrequently even in a more backward condition. The discharge of 

 the young iu these stages appeal's to me accountable for only in 

 this way — that from excessive heat the production of ova has been 

 very rapid (and the ovaries have been known to burst and the ani- 

 mal to die under these circumstances) ; the first eggs are, therefore, 

 involuntarily extruded from the inability of the animal to contain 

 the whole for the period necessary to the perfecting both of the 

 shell and internal organs of the embryo, and when this is the case 

 the young necessarily perish. 



When perfect, the young en masse are of a deep grey, or nearly 

 black tint, the stomach, heart, liver, and intestine clearly visible 

 through the transparent shell. The dark parts immediately at the 

 back of the ciliated pad become more developed, and being seen 

 more plainly through the transparent shells, is the cause of this 

 darker tint. 



By putting a little carmine into the water the functions of all 

 the organs are beautifully seen, and they are found as perfect in 

 the young as in the adult oyster. 



The projecting pad, with its cilia, serves both for propelling and 

 feeding, the oyster moving forward with open shells and expanded 

 mantle, into which the cilia draw the more minute objects which 

 form the food of the oyster, among which I have found most of the 

 marine species of diatomacese, and some few crustacege. In the 

 claires of Marenues, where oysters are green, I found the most 

 plentiful to be Achnanthes longipes, and Surirella ovata, whilst at 

 Hayling the greenness appears to be caused by the presence, in 

 immense numbers, of Gyrosigma formosa* 



The question whether an oyster is capable of self-impregnation is 

 one of the utmost importance. Upon it hinges the problem as to 

 improving the races by judicious crossing, which is obviously im- 

 possible if each oyster breeds without assistance from another. On 



* The distinctive colour of recent diatoms is brown. — Ed. 



