BIRTH, GROWTH AND REPRODUCTION OF OYSTERS. I I I 



even without one, a curious ramified and more or less 

 reticulated whitish marking, which is very obvious in the 

 breeding season, is observable beneath the thin tegument. 

 By appropriate methods of investigation, it is easily deter- 

 mined that this marking is produced by the ramifications 

 of a tubular organ, the reproductive gland, the trunk of 

 which debouches into a cavity common to it and the renal 

 organs, which again, it will be recollected, communicates 

 by a narrow slit with the supra-branchial chamber. The 

 trunk of the gland, on each side, passes upwards and back- 

 wards, in front of and above the adductor muscle, and 

 gives off a multitude of branches, some of which cross the 

 middle line and become inextricably united with those of 

 the other side ; while others form a network beneath the 

 skin, which covers the stomach and the liver. From this 

 network, blind offshoots are given off perpendicularly 

 inwards, and extend for a variable depth into the interior 

 of the body. The whole extent of the walls of the tubes 

 of this reproductive gland is lined by nucleated cells, and 

 it is by the metamorphoses of these cells that the ova, on 

 the one hand, and the spermatozoa, on the other, are pro- 

 duced. 



During the breeding season, an examination of the 

 adult oysters on an oyster bed shows that the number of 

 individuals, the reproductive glands of which contain 

 hardly anything but ova, is about equal to that of the indi- 

 viduals in which the reproductive gland contains hardly 

 anything but spermatozoa. I say "hardly anything," 

 because competent observers have affirmed, that careful 

 search will always reveal a few spermatozoa, in the former, 

 and a few ova, in the latter. Whether this be so or not, 

 there can be no doubt that, practically, oysters, while actu- 

 ally breeding, are either males or females. 



