908 REPORT OF COMMISSIONER OF FISH AND FISHERIES [18] 



Tlie existence of such a filament, however, seems very probable to me. 

 This byssus would therefore serve, as in the JSinnites, as a temporary 

 means of adhesion, and would soon give place to new shelly matter, 

 which is deposited along the edge of the shell, and which, while forming, 

 solders the larva to the collector. If no trace of a byssus is found in 

 the grown oyster this is not a serious argument against its existence in 

 the larva, for it isnot found in grown specimens of Unio and Aiiodonta, 

 which have a byssus in the larval stare.^*^ 



If one examines the structure of the secondary shell of a small oyster 

 which has been fixed for some days, it will be seen that it is not com- 

 posed of homogeneous layers as in the larva ; but that it i)resents a 

 reticular structure, and is composed of small prismatic columns of lime, 

 separated from each other by an organic substance (conchyoline) (Figs. 

 19 and 20). The diameter of one of these columns is about 0.012 milli- 

 meter. They are of a granulous character, as if they had been formed 

 of small globules, one resting upon the other. These prisms, however, 

 are not formed at the extreme edge, i. e., in the most recent portion of 

 the shell, where nothing is seen but a network of conchyoline, whose 

 meshes are not yet filled (Fig. 20). 



As is well known, the outer portion of the shell of the grown oyster, 

 of the Margaritana and others, also presents a prismatic structure. If 

 in the Margaritana the lime is removed from these prisms, nothing re- 

 mains but the walls around the columns, which seem to be comj)Osed only 

 of organic matter, and a small and insignificant organic remnant of 

 the prisms.^" According to Hessling, these layers are formed by a de- 

 posit of carbonate of lime in the prismatic cavities of the numerous thin 

 layers of conchyoline.^^ The empty meshes which I have described 

 above, and which are formed at the extreme edge of the little oyster 

 shell, as well as the observations made by TulFoerg on the shells of the 

 Margaritana^ speak strongly in favor of this opinion. The dark lines 

 seen in Fig. 19 inside the shell seem to me to be nothing else but fila- 

 ments of conchyoline ; at least in breaking the shell of a small living 

 oyster, I saw numerous gelatinous filaments between the mantle and 

 the extreme edge of the shell.^^ 



s^As, according to the observations of Boucbon-Braudely, the Portngnese oyster, 

 which is unisexual and whose eggs can therefore be fecundated artificially, adheres 

 to some object a couple of days after fecundation has taken place, I had hoped to be 

 able to have a better chance of studying its mode of fixation. Through the kindness 

 of Mr. Tripota, of Vernon, I received about 50 specimens of this oyster, but the \\n- 

 favorable weather which we had during the month of July was probably the cause 

 that the larvae, although theybegau to develop, did not adhere to any object. 



^'Tycho Tulberg : Sludien ilber Ban und Wachstlnim des Hvmmtrjyanzers und der 

 Molluskenschalen, in Kongl. JSvensk. Feisk. Acad. Ahli., vol. 19, 1882. 



3»Th. von Hessling: Die Perlviuscheln, 1859, p. 260, vol. v, Fig. 3. 



39 This report was already in the press when I came across an article by Mr. Osboru: 

 "On the structure and growth of the oyster shell" (Studies from the Biological 

 Laboratory, .Johns Hopkins University, vol. ii, No. 4). By the advice of Dr. Brooks, 

 Mr. Osborn studied the formation of the oyster shell, by boring in the edge of the 



