THE GENERATIVE OEGANS OF THE OYSTER. 273 



always present the same appearance. Omitting all reference to 

 diseased organs, the condition observed may always be classed under 

 one of the five heads following. 



"1. Abundance of ripe spermatozoa and scarcely any ovules. Early 

 stages in spermatogenesis rare. Everything seems to concur in the 

 production of as many spermatozoa as possible. The oyster fat. 



'^ 2. Spermatozoa ripe and in course of development. Ovules 

 pretty numerous on the walls of the follicles, but not a single ovum 

 ripe and in a condition to be fertilized. Oyster pretty fat. 



" 3. Spermatozoa in the course of development everywhere, and 

 here and there a little mass of ripe spermatozoa. A single ovule 

 still remaining on the wall of the follicles. Oyster thin. 



" 4. Abundance of ripe or nearly ripe ova (in condition to be 

 fertilized) both on the walls of the follicles and free in their 

 cavities. Among the ovules on the walls of the follicles some very 

 small cells whose nature could not easily be distinguished. No 

 spermatozoa. Oyster very fat. 



'' 5. Abundance of ripe or nearly ripe ova. Ripe spermatozoa in 

 the efferent ducts and in the primary lateral ducts leading into it. 

 No younger stages of spermatozoa. Cellular elements among the 

 ova on the walls of the follicles as in the previous case. Oyster 

 very fat." 



It should be added that the oysters in the second category show 

 differences both in the number and condition of development of the 

 ovules, but Dr. Hoek never saw ova in a condition for fertilization 

 alongside of ripe spermatozoa, unless indeed Case No. 5 is a question. 



As for No. 3, it must be added that the preparations of these 

 oysters corresponded exactly with those made from oysters which 

 were known with certainty to have had brood in their gills from one 

 to four weeks before being opened. 



Two facts may here be noticed which are of the greatest impor- 

 tance for the physiology of the organs of generation of the oyster. 

 These are : 



1. That the ova of the oyster at the moment of their escape from 

 the genital aperture are already fertilized, and that they have already 

 passed through the earlier stages of segmentation. 



2. That on several occasions spermatozoa have been found sur- 

 rounding the edges of the urogenital aperture as well as in the ter- 

 minal portion of the genital duct, in the ureter, and even in the renal 

 chamber. 



When it is considered that autogamy, or the faculty of self-fertili- 

 zation, is extremely rare in the animal kingdom, and that the nearest 

 allies of the common oyster {Ostrea virginica according to Brooks 

 and Ryder, Ostrea angulata according to Bouchon Brandely) are 



