BULLETIN OF THE UNITED STATES FISH COMMISSION. 1'jO 



A CONTRIBUTION TO OUR KNOWLEDGE OF THE DEVKLOPMEIVT 

 OF I III: OYSTER (OSTRE1 i:»IMM I,.). 



By DR. R. HOBST.* 



Duriug the past summer, as our zoological station was then estab- 

 lished in the vicinity of the oyster banks in the Eastern Schelde, I 

 busied myself for several weeks with the study of the history of the 

 development of the oyster. Even though this investigation is still in- 

 complete, I think, however, that the following communication may con- 

 tribute to an increase of our still very fragmentary knowledge of the 

 embryology of the bivalve mollusca. These investigations were carried 

 on in the station at Wemeldinge,t where, during my stay, I experienced 

 many disinterested and important favors at the hands of MM. Zocher 

 and De Leeuw. The study of the history of the development of the 

 oyster is beset with peculiar difficulties, to which the French zoologist, 

 M. Lacaze-Duthiers, alludes as follows: "The oyster is certainly one of 

 the most difficult of the species of the group of acephalous lamellibranchs 

 to study, both in relation to its organization as well as its development."! 

 While in the case of most of the lower animals the sexes are confined 

 to 'distinct individuals, and the sexual products, when mature, freely 

 escape from the body, the fertilization taking place outside the latter, 

 with the oyster this is not the case. Xot only do the embryos pass 

 through their first stages of development within the mantle cavity of 

 the adult, and impregnation occurs internally instead of externally, but 

 it may also be said that the eggs and spermatozoa come into contact in 

 their passage out of the generative glands. If it is desired to observe 

 the first changes of the fertilized egg, it is therefore impossible to resort 

 to artificial impregnation as in the case of most other lower animals, and 

 one is obliged to trust to finding individuals which are full of brood, which 

 may be opened for the purpose. If a mother oyster is opened in the 

 usual way, that is, by cutting through the adductor muscle, the animal 

 soon dies, and the normal development of the brood which it contains 

 is also disturbed; for one may keep the embryos alive in an aquarium 

 for several days, though abnormal conditions soon make their appear- 

 ance, if the development itself does not come to a complete standstill. 

 Lacaze-Duthiers observes that he kept oyster larvae alive in aquaria 

 longer than a month, but he affirms that during all of this time slow 

 changes of organization occurred, which it is safe to say were not nor- 



* Bijdrage tot de Kermis van de Outwikkelingsgeschiedenis van de Oester (Ostrea 

 edulisL.), door Dr. K. Horst, in Utrecht. Extracted from Tijdschr. d. Ned. Dierk. 

 Vcreen, dl. vi, 1882. Translated by J. A. Eyder. Abstr. in Zoolog. Anzeiger, 3d 

 April, 1882. 



tSee the 6th yearly report (Jaarverslag) of the zool. station.") 



X Me"ni. sur le developpement des ac6phales laniellibranches. (Comptes rendu, 

 cad. Sc, Paris, t. xxxix, p. 1197.) 



