THE GENERATIVE ORGANS OP THE OYSTER. 269 



siderable of wliicli passes forward for a short distance^ curves over 

 tlie oral process, and supplies the posterior part of the gills. It is 

 shown in fig. 1. If this nerve is carefully examined in its course 

 over the oral process, a slit may be distinguished, lying close and 

 pai'allel to it, on the oral process. This slit — which may be seen on 

 both the right and left sides of the oral process — is the urogenital 

 aperture. 



Fig. 2 is a diagram to exhibit the relations of the organs which 

 open on each side of the body by the urogenital apertures. The 

 so-called kidney or organ of Bojanus, first discovered and described 

 by Dr. Hoek, is represented in shading. Its structure need not 

 detain us ; it is sufiicient to say that it is a paired organ, and that it 

 communicates on either side of the body with the pericardial cavity 

 by a canal, marked Rp.C. in fig. 2. The generative organs are re- 

 presented by thick black lines, but are shown smaller than they 

 actually are to avoid encumbrance of the figure. 



Like the organ of Bojanus, the reproductive organ is paired, but 

 its branches interlace and anastomose to such an extent that the 

 two members of the pair become confounded with one another, and 

 the paired apertures are the only evidence of the double character 

 of the organs. 



Two portions may be distinguished on either side, the reproductive 

 organs properly so called, and the genital duct. There are no 

 accessory organs, such as yolk-glands. 



The generative organs may most conveniently be studied in a 

 year-old oyster. The genital duct opens into the anterior part of 

 the slit-like urogenital aperture. At a short distance — half a mille- 

 metre, for example — from its opening the duct begins to give off a 

 number of culs-de-sac, which are placed perpendicularly to the 

 direction of the duct, and are nothing more than outgrowths of its 

 wall which project into the surrounding connective tissue. The 

 epithelium of the wall of the canal is continued along the walls of 

 the outgrowths, but the cells are not provided with vibratile cilia 

 and are not distinctly marked off from one another. It appears that 

 at a subsequent period they multiply and become metamorphosed 

 into generative products, ova or spermatozoa. If the genital duct 

 is followed further forw^ard to the pericardial cavity, a number of 

 similar canals are seen to originate as outgrowths of the genital 

 duct. These lateral canals penetrate into the connective tissue of 

 the oral process or spread out parallel to the surface of the oyster. 

 In the former case the genital products are developed on both sides 

 of the canals, in the latter case only on that side opposite to the 

 surface of the body. In the latter case the wall of the canal which 

 runs parallel with, and at a little distance from the surface of the 



NEW SERIES. VOL. I, NO. III. 20 



