HISTORY or TlIK OYSTER. 19 



" May 19. — Dissected and examined a large number 

 of oysters sent here (Eyton) from Burnliam, through 

 the kindness of Mr. Sweeting, of Chcapside, London. 

 The ovaries of all were slightly distended, and full of 

 spawn of various sizes, as represented in the plate 

 (PI. IV.), when seen in the microscope under a ^-inch 

 power. In the smallest I could not perceive any 

 motion ; but in the larger could distinctly detect the 

 vibratile ciKa or feelers, as they would probably be 

 termed by the fishermen, in active motion. The smaller 

 ones were round, with a dark marginal rim (PI. IV. 

 fig. 1), and some had indistinct lines radiating from 

 the centre towards the margin (PI. IV. fig. 2) : the 

 larger ones (PI. IV. fig. 3) were similar in shape to 

 those obtained from Loch Ryan on the 10th "of July, 

 IS 56, and exhibited to the British Association at 

 Cheltenham : the interstices between the bronchiae 

 and mantle were closely examined, but not a vestige 

 of an ovum was to be seen*. The oysters opened were 

 from 2^ to 3 inches in diameter, and had the smooth 

 shell of ' natives ' ; those most advanced towards 



* The spermatozoa with cilia are, I should suppose, un- 

 doubtedly the perfect young ; but what are the other rounded 

 bodies ? A few having been found with radiating lines, it 

 appears likely that a subdivision takes place in an early stage, 

 probably after fecundation. I did not see any spermatozoa 

 that I could construe into male spermatozoa ; but I think it 

 probable that they might be visible in the early part of the 

 year, before the ovary begins to sw-ell much. 



c 2 



