320 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



have. Its introduction and acclimation into our waters are due en- 

 tirely to an accidental cause. A vessel coming from Portugal brought 

 back a cargo. Entering the Gironde after a long voyage, the captain 

 thinking the oysters were dead had the whole ship-load thrown into 

 the water, on an old bed called the Banc du Richard. Having found in 

 the Gironde a medium almost identical with that from whence they 

 came, and the conditions favorable to their propagation, they have 

 there multiplied in such proportion that from the Pointe de Grave to 

 beyond Banc du Richard, that is for an extent of nearly 30 kilometers, 

 they form a vast bed, the extent of which will soon be limited only by 

 the banks of the river. 



The natural history of this mollusk has been imperfectly known, and 

 the accounts of it are very vague. We may compare them with the 

 common oyster, from which they differ as follows: 1, in their form; 2d, 

 in the taste of their flesh; 3d, in their habits; 4th, iu respect to their 

 sexuality. 



It is superfluous to here describe their external form, in that it does 

 not recall that of 0. edulis. 



As to the taste or flavor, no confusion is possible to a palate in the 

 least experienced. As to their habits, we know that they delight in 

 brackish and muddy waters, and that there they multiply in preference 

 to all other situations. We And them, in fact, in the Gironde, in the 

 approaches to the lie d'016ron, at the mouth of the Charente, where 

 the waters have a specific gravity of between 1£ to 3 degrees (1.009 to 

 1.020). They still multiply in the Basin of Arcachon but meagerly, and 

 only in such places where they are sensible of the influence of fresh 

 w r ater. It is fitting iu this connection to allude to a singular phenome- 

 non at that place; it is, that the oyster of the Tagus there becomes 

 infertile after a certain length of time, to such an extent that they soon 

 disappear in the basin if a complement of sexually mature individuals 

 are not brought there at intervals to perpetuate the species. 



In respect to sexuality, the difference between these two mollusks is 

 very great ; most radical. Ostrea edulis is hermaphrodite ; O. angulata 

 is unisexual or dioecious. We have opened more than 10,000 in all 

 phases of reproductive activity, and we have not seen a single one of the 

 latter of which the sex was doubtful. They were all either exclusively 

 male or exclusively female. 



No less marked is the difference in the mode of reproduction. The 

 eggs of the common oyster are fecundated within the valves of the 

 parent, apparently within the openings of the oviducts; those of the 

 Portuguese species on the bosom of the waters. The first cannot de- 

 velop outside of the incubatory cavity of the parent; the second undergo 

 their development in the open currents. The larvae of O. edulis, iu order 

 to live, develop and attain the errant or pelagic stage of their existence, 

 are dependent upon the albuminous liquid secreted by the mother; 

 those of O. angulata, more vigorous, more independent, and altogether 



