MOLLUSC A. 



29 



but it seems certain that the organs of generation are simi- 

 lar in all specimens, and that most observers are inclined 

 to believe that the generative organs are filled in some 

 specimens exclusively with spermatozoa, and in others ex- 

 clusively with eggs. This seems to show that the sexes 

 are distinct in the oysters, though the organs of generation 

 are similar. The orifice for the exclusion of the eggs and 

 spermatozoa is situated at the black mark in Fig. 15, w" ; 

 and from this a branching tube connects with all parts of 

 the ovary. 



Just under the generative organs, and in one place near 

 the mouth uncovered by them, lies the dark, brownish- 

 green liver, composed of grape-like bunches of glands con- 

 nected by hollow branches, which unite into stems and 

 -empty bile into the blind sacs of the stomach (Figs. 2, 

 12, /). Within the liver and generative organs lies the 

 coiled alimentary canal, surrounded by its coat of blood 

 vessels, which in places form a very thick, spongy, invest- 

 ing mass. 



The situation of the mouth we know already. The 

 throat, or aesophagus, is very short, leading immediately 

 into the stomach, a large sac (Fig. 12, sf), with several 

 deep blind sacs, into which the branches of the liver 

 organs empty the bile. The intestine begins at the pos- 

 terior end of the stomach, and passes first posteriorly be- 

 tween the great muscle and the gills, where it makes a 

 sharp return to the right. From thence it keeps to the 

 right, running dorsally, and passes under the intestine and 

 stomach to the left. Near the mouth it makes a bend to the 

 left, passes under the mouth, and then (Fig. 2) ventrally 

 on the left side, describing a half circle, again skirting the 

 bases of the palpi and the gills. 



When far enough around, it reverses the curve, and 

 passes out of the visceral region across the cavity contain- 

 ing the heart on to the dorsal side of the great muscle, 

 where it terminates. 



