276 THE GENERATIVE ORGANS OF THE OYSTER. 



also exercise an unfavorable influence on the age at whicli the 

 animal begins to breed, so that a considerable number of natural 

 oysters a year old might produce ripe ova and spermatozoa, whilst 

 this might never be the case, or at least might be very exceptional, 

 in cultivated oysters. The question can only be settled by further 

 observation., Particularly it is necessary to compare cultivated and 

 natural oysters. It is probable that it will be found that cultivated 

 oysters differ greatly among themselves, since the brood, fixed in the 

 summer, and usually detached in the spring months, is not always 

 treated in the same manner. If the collectors with the young brood 

 are placed in the sea for the winter, and if afterwards the young are 

 left on the collectors, the oysters are flat and too much crowded ; 

 they have a low market value, but in the development of their gene- 

 rative organs they approach much nearer to natural oysters than do 

 cultivated oysters. 



The more a cultivator deviates from the course followed by nature 

 the greater the danger of weakening the reproductive capacity of the 

 oyster. It is certainly a considerable deviation to place the collectors 

 in ponds during the winter. To detach the oysters from the collectors 

 is another deviation ; a third is the crowding of hundreds of oysters 

 in small reservoirs ; a fourth to keep young oysters for a whole year 

 in pares, &c. Although many of these deviations do not appear to 

 be dangerous to the life of the nurselings, and are even necessary 

 to the advantageous application of culture, one must not lose sight 

 of the fact that they must necessarily exercise an unfavorable in- 

 fluence on the reproductive faculty. 



It may be added that among cultivated oysters those of the fourth 

 and fifth year are the most prolific. Oysters six years old still have 

 well-developed reproductive organs, but in oysters of nine or ten 

 years they are always poorly developed, and rarely contain genera- 

 tive products. The liver too, in these last is greatly enlarged, so 

 that the layer of connective tissue between it and the body-wall 

 which contains the follicles of the reproductive organs, is of very 

 slight thickness. Ordinarily the follicles of these aged oysters 

 contain no ova, but a few spermatozoa. The conclusions arrived at 

 by Dr. Hoek in the course of his work are as follows : 



A. Anatomical.^ 



1. The reproductive organ of the oyster consists of a genital gland 

 and efferent ducts. There are no accessory organs. 



* Several of the anatomical conclusions arrived at by Dr. Hoek are omitted, as being 

 beyond the purpose of the present abstract. 



