278 THE GENERATIVE ORGANS OF THE OYSTER. 



7. The number of oysters producing spermatozoa is^ in the East 

 Schelde^ greater than those producing ova. 



8. The ova of a ripe oyster are laid all at once, excepting a few 

 which are ill developed. The production of spermatozoa probably 

 for a longer period. 



9. In every oyster examined the production and emission of ova 

 was followed by a period in which only spermatozoa were formed. 



10. A large portion of the brood which attaches itself every year 

 on the banks of the East Schelde is not, in all probability, derived 

 from the oysters in the establishments. 



11. It would appear that cultivation exercises an unfavorable 

 influence on the fertility of oysters. 



12. In aged oysters the liver is much more developed than in 

 young. This development is correlated with the retrograde condi- 

 tion of the reproductive organs. 



A Comparative Examination op Cultivated and Natural Oysters, 



MADE to determine THE NUMBER WHICH ANNUALLY TAKE PaRT IN 



Reproduction.'^ 



After the publication of his first paper, Dr. Hoek received from 

 Baron Groeninx van Zoelen and Baron G. H. Clifford, oyster culturists 

 of the East Schelde, an offer of a sufficient number of oysters for the 

 continuation and completion of his researches. This offer he will- 

 ingly accepted, and received towards the end of June, 1883, 200 

 oysters from an establishment where only cultivated oysters had been 

 laid down, and 200 others from a locality where no cultivated 

 oysters had ever been laid down. The age of every oyster was 

 noted, and also whether it had been growing on a tile, a shell, or a 

 stone. Each individual was numbered, and a piece was taken and 

 preserved in alcohol for further investigation. A thin section was 

 eventually made from each piece, which was stained and treated for 

 microscopical examination. 



The oysters examined were opened between June 16th and 28th, 

 and as the pieces removed were immediately placed in spirit, subse- 

 quent examination of them gave an exact idea of the condition of the 

 sexual organs on the day on which they were opened. In several 

 cases the examination of these pieces was not wholly satisfactory. 

 Some of the oysters had spat in their beards ; these might have been 

 pronounced as functional females for the current year without any 

 further examination : some others contained a great number of ripe 



* Dr. P, p. C. Hoek, Tijdschrift der Nederlandsche Dierkundige Vereeniging, Sup- 

 plement Deel i, Aflevering ii, 1883-4, p. 483. 



