BTEEB) LIFE-HISTORY OF THE OYSTER. 327 



March and April. Upon examining large numbers of individuals at the 

 same period, it will be found that while in many specimens rejiroduc- 

 tive activity has quite ceased, in others it is still iu active progress. 

 This variation is doubtless due to variations in the amount of food and 

 to favorable temperature conditions, but it is in the highest degree 

 probable, judging from the appearance of the spat, that comparatively 

 few embryos ever develop so as to come to anything, except during 

 the summer months. 



The superficial extent of the reproductive organs is quite considerable, 

 as may be inferred from au inspection of Fig. 4, which represents the 

 soft parts of an oyster viewed from the left side, to display the ramifi- 

 cations of the generative ducts of the left half of the body, and the 

 outlet below the muscle at ov. The generative tissue Gen, in this figure, 

 is distributed over the surface of the body-mass as a thick, creamy 

 white, superficial layer which covers the greater portion of the latter. 

 It really consists of a multitude of little sacs or follicles embedded in 

 the connective tissue, which open and pour their contents into the su- 

 perficial branching ducts shown in Fig. 2. The mature products are 

 poured out of the large oviduct ov, which empty into the water space 

 above the gills, the current from which passes out of the shell by way 

 of the cloaca cl (Fig. 1), which carries the generative products outward 

 into the open water in the case of the American and Portuguese species. 

 In these two species the impregnation appears to occur outside of the 

 parent iu the open water, where the eggs and mQt encounter each other 

 from individuals of different sexes, but in the common European species 

 the unanimous testimony of observers is^ to the effect that the young 

 are retained within the parent shell, adhering iu masses to the mantle 

 and gills, where they undergo a kind of incubation, prior to being set 

 free to shift for themselves. This is a remarkable difference of habit, 

 and one which would alone serve very well to discriminate the two forms 

 from each other. The embryos of the hermaphroditic species are about 

 twice as large in diameter as those of our native and the Portuguese 

 species, owing to the fact that there is about the same difference iu the 

 size of the mature ova of the two types. 



It is remarkable that we should find the reproductive organs of the 

 oyster much more developed in some individuals than iu others'; iu fact we 

 may find them apparently wanting altogether in some specimens after the 

 spawning season is over, or, on the other hand, forming, in the height of 

 the season, a layer over the outside of the body-mass more than a fourth 

 of an inch in thickness in some places. In an undeveloped condition 

 the generative ducts and follicles form an open network which traverses 

 the connective tissue. The relations of the generative tissues to the^ 

 other organs is very well shown in Fig. 3, where ge indicates this layer 

 moderately developed, as seen in a cross-section. Judging from the 

 many observations made by the writer, it is evident that these organs 

 diminish greatly in bulk, or disappear entirely after the spawning season 



