Feb. 1, 1865.] THE TECHNOLOGIST. 



THE TINNEVELLY PEARL-BANKS. 299 



and to eradicate the evils caused by sand accumulations and dead 

 molluscs, owing to their great depth and exposed situation in the open 

 sea at a distance from land. Unless some plan is adopted for rearing 

 the young fish on banks which shall be constantly accessible and free 

 from the above drawbacks, the fishery will always be liable to failures, 

 sometimes of long duration. The perfection to which science and 

 intelligent care have brought the fisheries of edible oysters on the 

 English, and especially on the French coasts, leaves no doubt that 

 equally satisfactory results might be obtained from similar measures on 

 the Tinnevelly pearl-banks. 



A. few remarks on the habits of the pearl oyster will make this part 

 of the subject more clear. 



It is, perhaps, unnecessary to observe that the pearl oyster 

 (Meleagrina margaritifera, Lam.) is not in reality an oyster at all, but 

 seems more allied to a mussel, having, like the latter animal, a byssus 

 or cable, by which it secures itself to the rocks — one of the most 

 important points in its organization. The animal's foot is composed of 

 muscular fibres, and is 2\ inches long when distended. On the lower 

 side there is a groove lined by a secreting membrane, which is an exact 

 mould for the formation of the byssus. When the animal desires to 

 attach itself to the rock its foot is protruded, and, after seeking out a 

 suitable spot with the tip for some minutes, is again retracted into the 

 shell. A strong fibre, of the form of the groove in the foot, is thus left 

 attached to the base of the foot at one end, and to the rock at the other. 

 The process is again and again repeated until a strong cable is formed ; 

 and it was one of the most important results of the careful investigations 

 of Dr. Kelaart in Ceylon, that the power to cast off its byssus at pleasure 

 was ascertained. It leaves it behind to make another in a more con- 

 venient place, like a ship slipping her cable and going to sea. From 

 this ability to shift its berth it follows that the pearl oyster might safely 

 be taken from its native beds and made to colonize other parts of the 

 sea ; and also that it would move of its own accord if the surrounding 

 water should become impure or sandy, or when there is an influx of 

 fresh water. The animal can reform the byssus at pleasure, if in good 

 health and condition. 



The formation of pearls is another point which has received muchatten- 

 tion, but which has not as yet been definitively settled. Pliny and Dios- 

 corides believed that pearls were productions of dew, but that observant 

 old Elizabethan navigator, Sir Rich. Hawkins, shrewdly remarked that 

 "this must be some old philosopher's conceit, for it cannot be made pro- 

 bable how the dew should come into the oyster." Modern investigation has 

 suggested various causes for the intrusion of the nucleus round which 

 the pearl is formed. The free border of mantle lining each valve of the 

 shell dips downwards to meet a similar edge on the opposite side, thus 

 forming a double-fringed veil. The tentacles of this fringe consist of 

 long and short flat filaments, which are exceedingly sensitive,- so that 



