274 THE GENERATIVE ORGANS OP THE OYSTER. 



unisexual, one can hardly escape the conclusion, in face of the facts 

 above mentioned, that the oyster is at the moment of propagation a 

 functionally unisexual animal. One could not otherwise explain the 

 different conditions in which the generative organs are found during 

 the breeding season. M. de Lacaze Duthiers, it is true, has found 

 a few ova in oysters filled with semen, and a few spermatozoa in 

 oysters filled with ova, but in the former case the spermatozoa could 

 hardly be destined to fertilize such a very small number of ova, 

 which are besides unripe ; and in the latter case the number of sper- 

 matozoa found by him are altogether insufficient for the fertilization 

 of the ripe ova contained in the animal. Further, it must be remem- 

 bered that not only is it impossible that two oysters should copulate, 

 but that it is equally impossible that the generative products of the 

 two sexes should be brought together when floating freely in the 

 sea; for how if this were the case could the development of the 

 brood in the gills of the mother be explained ? Nobody has attempted 

 to deny that the brood contained in the gills of an oyster is derived 

 from that oyster. It is impossible to believe that it could collect 

 in its gills a number of ova from the surrounding water, when those 

 ova, being denser than the water, do not float. At the moment of 

 their exclusion the ova are fertilized, and as soon as " white spat " 

 is observed in the gills of an oyster, its generative organs are found 

 on examination to be empty and exhausted. Clearly the white spat 

 in the gills has been produced by the same individual in which it is 

 found. The spermatozoa by which those ova are fertilized might 

 be produced by the mother oyster itself, or might be derived from 

 another oyster. The former supposition is sufficiently refuted by 

 the fact that the reproductive organs of a ripe oyster are either 

 entirely filled with ova, or nearly entirely filled with spermatozoa. 

 The fertilizing spermatozoa must therefore be derived from other 

 oysters. 



The only possible conclusion is that during the breeding season a 

 number of oysters produce and emit such a large quantity of sper- 

 matozoa that the water passing over an oyster-bed is charged with 

 them, and that a sufficient quantity are able to penetrate into the 

 mantle cavities, and thence into the bodies of the ripe females, and 

 thus fertilize their ova. The number of spermatozoa which are lost 

 must of necessity be much greater than those which are utilised. 

 In the only case in which the two genital products are found side 

 by side and perfectly ripe in the reproductive organs the sper- 

 matozoa are all free, none are united into masses, and they are only 

 found in the main genital duct and its principal branches, which is 

 evidently in favour of the view that they have found their way there 

 from without. 



