[9] DEVELOPMENT OF THE OYSTER. 899 



of the glass vessels in which they were. They became so firmly fixed 

 that a strong current of water could not detach them. He could not 

 discover with any degree of certainty in whatmauner they were attached ; 

 but, although he admits the possibility of the existence of a filauientous 

 byssus, he supposes that the fixation takes place by means of the edge 

 of the mantle which protrudes from the shell ; because he has often 

 seen the larva resting on its side, and the edge of the mantle protrud- 

 ing from the valves. Before the larval period comes to an end the 

 straight line of the hinge disappears more or less as the shell growth. 

 When the larva has become fixed, new layers of shelly matter are de- 

 posited round the edges, presenting a prismatic structure. During this 

 growth the hinge end is slightly lifted up, so that it is clear that shell 

 matter is deposited along the edge. The lower valve is so firmly attached 

 to the collector by the organic matrix of the shell (the conchyoline) that 

 it cannot be torn from it without breaking it. 



II. — Personal Eesearches. 



These observations were made during the summers of 1881 and 1883, 

 at our branch station of Wemeldinge,^^ where I received all the assist- 

 ance that could possibly be rendered from Messrs. Zocher and De 

 Leeuw. The parks found in the neighborhood, in which the larvae of 

 the oyster were allowed to affix themselves, proved very useful for my 

 researches. The study of the development of the oyster is beset with 

 difficulties, which has led Professor De Lacaze-Duthiers to say with 

 good reason that '' the oyster is certainly one of the species of the group 

 of the acephalous lameUibranchiata, the jstudy of whose organization 

 and development is exceedingly difficult." ^^ With most of the lower 

 grades of animals the sexes are separated, and the sexual products, 

 when mature, are ejected ; consequently fecundation takes place outside 

 of the body. It is entirely different with the oyster. Not only do its 

 embryos pass the first stages of their development in the mantle cavity 

 of the mother oyster, and fecundation takes place inside and not out- 

 side, but the eggs and the spermatozoa probably meet in the excretory 

 canals of the sexual gland. If one wishes to observe the first changes 

 of the fecundated egg, this cannot be done, as with most of the lower 

 grades of animals, by artificial fecundation 5 but one is obliged to open 

 a certain number of oysters containing eggs. If one opens a mother 

 oyster in the ordinary manner — that is, by cutting the adductor muscle 

 of the shell — it soon dies, and the normal development of its offspring is 

 consequently disturbed. Embryos separated from the mother oyster 

 may be preserved alive in an aquarium, but they either soon become 

 sick or their developmeut stops entirely. Thus Professor De Lacaze- 



18 See tlie Sixth Annual of the Zoological Station. 



^^ M^moire sur le diveloppetnent dea Acephales lamelUhranches. lu Compt. Rend., Purls, 

 vol. xxxix, p. 1197. 



