270 THE GENERATIVE ORGANS OF THE OYSTER. 



body, is composed of an epitlielium provided with vibratile cilia quite 

 similar to that of the genital duct, of which it must be considered as 

 a continuation. 



In front of the pericardial cavity it becomes difficult to follow the 

 genital duct. It divides into several branches, which spread on the 

 surface of the body, and, like the outgrowths of the first part of the 

 duct, run for a short distance parallel with the surface of the body. 

 All these canals are oval in section, and their outer and inner walls 

 differ in minute structure ; the outer wall is lined with a ciliated 

 epithelium, whilst the epithelial cells of the opposite wall are evi- 

 dently already in the process of transformation into generative pro- 

 ducts. 



The canals themselves are placed at considerable distances from 

 one another. Their interior walls often show the commencement of 

 a number of culs-de-sac, which enter the surrounding connective 

 tissue. The culs-de-sac seem always to be longest near the genital 

 aperture, and decrease in size and development the further they are 

 from it. 



In a ripe oyster several changes have taken place. The growth 

 of the whole body is accompanied by a growth of the lateral branches 

 of the genital duct, both in length and in size. The number of the 

 branches is much increased, and they anastomose to form a net- 

 work of branches and branchlets on the two sides of the body of 

 the oyster, which is not the case, as far as can be as ascertained, 

 in a yearling oyster. Extending still further, the branches of the 

 two sides of the body unite and anastomose. At this stage the 

 generative organs nearly surround the trunk in front of the 

 adductor muscle. They lie near the surface, but are separated from 

 it by a thin layer of connective tissue, and are continued by the 

 anastomoses of the network of either side, over the anterior and pos- 

 terior surfaces, but are more conspicuously developed on the poste- 

 rior than on the anterior surface. 



The productiveness of the generative organs is dependent on the 

 increase of their surface. This is attained not only by the multi- 

 plication of their branches, but also by the growth of the walls of 

 each branch. That part of the wall of each canal which is opposite 

 to the surface of the oyster increases greatly, and penetrates into 

 the connective tissue. These outgrowths, at first small, grow longer 

 afterwards, but remain comparatively small as long as the genital 

 products are not ripe. Their extent continues to increase, both 

 because they become individually larger and because the number of 

 branches is considerably augmented, until in the breeding season the 

 maximum development is found in oysters of four and five years old, 

 in which the follicles and their ramifications form a layer several 



