15 



The generative organs of tlie oyster, Gen. Fig. 2, are 

 massive in proportion to the size of the animal ; they 

 invest the whole of the visceral mass from a little be- 

 hind the palps to the pericardial space, extending beyond 

 it posteriorly above and below. They invest the rectum to 

 within a short distance of the vent and the first bend of 

 the intestine below the adductor muscle ; their substance 

 also dips down deep amongst the viscera so as to appear 

 to cover the intestines, the pouch of the crystalline style 

 and the liver. The sexes of the oyster are distinct, but 



\ 9 r'*- 



Figure 2. 

 there is no apparent possibility of determining the sexes 

 from the external appearance of the generative tissues, 

 since there seem to be no differences between what in 

 one case are ovaries containing eggs, and in another 

 spermaries or testes, containing the male cells or sperm- 

 atozoa. Both kinds of glands are composed of a great 

 number of tubular branches which unite into two large 

 canals, one on each side of the body, which open into 

 thr upper gill cavity at ov / the oviducts if the specimen 

 be female, and vasa defer entia if the specimen be a male. 

 The smaller branches divide and subdivide, as may be 

 noted in Fig. 2, giving off ultimately short blind, x^ouch- 

 like branches, which are the follicles of the glands or 



