[17] DEVELOPMENT OF THE OYSTER. 907 



with a thin layer of hydraulic cement, which is generally used in cover- 

 ing the tiles. The result was that the apparatus answered its purpose 

 admirably. The slides were left in the water 72 hours, and several 

 larvae became attached to them. Most of them were on the pieces of 

 glass covered with lime, some on the rough glass, and only two on the 

 common glass. 



Microscopic examination shows that, during this period, the larva of 

 the oyster is fixed on the collectors almost vertically, so tluit the hinge is 

 at the top, and turned toward the observer (Fig. 18). The shells, which 

 measures 0.24 millimeter in height, has still a homogeneous structure 

 in the larva; and there may still be seen distinctly the little teeth at 

 the hinge, traced in a straight line'. Later these characteristics dis- 

 appear more and more (Fig. 19) because the valves of the shell grow 

 over or overhang the edge of the hinge, so as to form a swelling (umho). 

 The opinion of Mr. Ryder^* that the hinge has no teeth, contrary to the 

 observations of De Lacaze-Duthiers, may be true as far as the American 

 oyster is concerned, but it does not apply to the Ostrea edulis, as I have 

 stated above. There is deposited, all along the edge of the shell of the 

 larva which is about to become fixed, a straight band of new shell sub- 

 stance, 0.012 millimeter broad, which shows the structure of the grown 

 or secondary shell. This little band of secondary shell substance, 

 which is naturally secreted in a liquid state along the edge of the mantle, 

 may possibly have aided the little oyster in adhering to the piece of 

 glass. I regret that I am unable to solve this j)roblem satisfactorily. 1 

 believe that I have repeatedly and very distinctly noticed a small 

 byssus ; but the difficulties encountered in these investigations are so 

 numerous that, like Mr. Ryder,^-'' I have not been able to arrive at a 

 definite result. 



In the first place the almost vertical position of the little shell is very 

 unfavorable to these investigations ; moreover, the larva but rarely ;h1- 

 heres to smooth glass, and is certain to do this only on glass covered 

 with lime. In order therefore to observe the small object with trans- 

 mitted light it becomes necessary to remove the lime, in which I suc- 

 ceeded pretty well ; for after the slide has been held for 5 or 10 minr.tes 

 in a solution of 1 per cent chromic acid, all the carbonate of lime lias 

 disappeared. By this treatment the carbonate of lime of the shell has of 

 course also been dissolved, which causes the young oyster to undergo such 

 modifications in its appearance, that this method has not been of any 

 assistance to me. If one takes into consideration also the circumstance 

 that all sorts of animalcules adhere to the young oyster and all around 

 it (such as Vorticella, Acinetians, &c.) ; and that all kinds of impurities 

 adhere to it, which cannot be removed by mechanical means without 

 injuring the young oyster, it will be acknowledged that it is exceedingly 

 difficult to ascertain whether or not there is a thin filamentous byssus. 



3* Bulletin of the United States Fish Commission, 1882, p. 384. 

 3sSee the preceding note. 



