Pearl Oyster and on the Production of Pearls. 83 



of a hand, or the shadow of a person, near the glass sides of a 

 vessel in which it is confined. I should not in a popular Report 

 advert to this physiological subject, but that the senses of the 

 oyster have a great deal to do with its habits, not only in the 

 aquarium, but also in its native bed. Were it not for these 

 delicate fringes surrounding the mantle, the softer parts of the 

 oyster would easily become the food of a host of carnivorous 

 creatures abounding in the sea ; and many more pearls would 

 drop out- of the shell than do now with such sentinels at the 

 entrance of its external rim. The mantle is the only organ the 

 animal has for the formation of the shell, the increase of the 

 lateral dimensions of which, and the formation of the pearly 

 nacre, and pearls, depend upon the condition of this important 

 investment. If it is injured, the pearly matter is not secreted 

 in such abundance over the shell, or if, by some cause, it be- 

 comes retracted, the shell does not grow rapidly, and the 

 mother-of-pearl lining is jagged at the edge, and is not of 

 the usual brilliant colour. However, its temporary retraction 

 facilitates the ingress of sand and other irritating particles, 

 which doubtless become the nuclei of many a pearl, as will be 

 hereafter observed. The fore part of the mantle is coloured and 

 rayed like the shell. The colouring matter is secreted by glands 

 found in these parts. This glandular secretion serves the pur- 

 pose of increasing the lateral and longitudinal dimensions of 

 the shell. It is after this is deposited, that the pearly secretion 

 (nacre) is applied to the inner wall of the shell, which, concreting 

 or solidifying, increases its thickness. The pearly fluid is se- 

 creted by nearly the whole external surface of the mantle. It 

 will be thus clearly understood that when a grain of sand or the 

 larva of an insect is introduced between the mantle and shell, it 

 will become covered over with the pearly secretion; which, 

 always going on, is augmented at that part where the foreign 

 matter lies. This phgenomenon I have detected, with the aid of 

 the microscope, in its very earliest stage. 



" About 1 J inch from the rim of the shell, is seen a pair of 

 gills, like four segments of a circle, or semilunar combs, stretch- 

 ing transversely from one side to the other, the convexity look- 

 ing forwards. There is a vacant space between the concave 

 surface of the gills and the body of the oyster. The adductor 

 muscle, called 'gristle,^ is now seen, covered over with a delicate 

 membrane. This muscle is attached to the inner surface of both 

 the shells. On one side (the left, when the oyster is placed 

 with the hinge next the observer) is seen a short, conical, tubu- 

 lar, sharp-pointed prolongation ; this is the terminal end of the 

 intestines : it looks like a sharp-pointed claw. The intestine is 

 short ; leaving the stomach, it winds round the adductor muscle, 



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