86 Drs. Kelaart and Mobius on the Natural History of 



or shorten the cable or byssus. The foot, in a full-sized oyster, 

 is about two and a half inches long when extended; at rest, it is 

 not more than one and a half inch in length. It is broad at the 

 base, tapering to a conical point ; the upper surface is rounded 

 and smooth, the lower flattened and grooved. The groove ex- 

 tending from the base, terminates at the point in an oval cup- 

 like fosset. This groove is lined by a secreting membrane, and 

 is an exact mould for the formation of the byssus, at the will of 

 the animal. When it finds a necessity for making one, the foot 

 is protruded out of the shell, and with the tip it seeks out a 

 spot where it can rest the terminal disc of the groove. If not 

 satisfied with the substance or position of the stone or any other 

 matter on which it rests, it removes to another more suitable 

 spot; for a few minutes (say five or six, if the animal is strong) 

 it rests, and is then retracted within the shell, leaving behind a 

 strong fibre with an oval disc, of the form of the groove in the 

 foot. This whitish fibre is attached to the base of the foot at 

 one end, and to the rock, or to the shell of another oyster, at 

 the other. In a day or two, this fibre becomes of a bronzed 

 greenish colour, and looks like hair, with a broad flattened oval 

 root attached to the rock This process is again and again re- 

 peated, at intervals of a few minutes, till a sufiiciently strong- 

 cable is formed. In a large oyster, removed from the sea, up- 

 wards of fifty such fibres form a thick strong cable or byssus, 

 which is attached to the base of the foot by a bifurcated fleshy 

 root. The animal cannot detach the byssus from the rock to 

 which it is attached, but it has the power of casting it ofi" its 

 own body and leaving it behind (like a ship letting slip her 

 cable and anchor in a storm, and sailing ofi* to sea), in order to 

 make another byssus, either on the same rock, or on any other 

 convenient place. 



" I observed all this process in the aquarium, at a very early 

 period of my investigations ; and was not surprised to find, that 

 the Pearl Oyster, having nearly the same organs as the Mussel, 

 should form and reform its byssus. But I was agreeably satis- 

 fied in learning by these observations, that Captain Steuart, in 

 his valuable and interesting ' Monograph on the Pearl Fisheries 

 of Ceylon,^ was incorrect in denying to the Pearl Oyster this 

 faculty. He states, that ' it is not believed that Pearl Oysters 

 have the power to detach themselves, or to remove at their own 

 wilU I have not only satisfied myself, and many friends who 

 have seen the oysters in the aquaria which I have established, 

 that the Pearl Oyster can detach or unmoor itself, but likewise 

 that it walks away with its foot foremost, and the shell behind ; 

 and does not, as Captain Steuart observes, ' move with its hinges 

 in advance,^ This ' shuffling ' movement alone attracted Cap- 



