THE TOMB OF PEARL 



concretions or cysts, not attached in any way. Hence 

 their regular shape, most often spherical, and the 

 pure smoothness of their surface. They are made of 

 fine concentric layers, and the light, playing in them 

 with more splendour, gives them that peculiar lustre 

 which is the source of their charm and value. But in 

 origin they are not the least different from the others. 

 There is a little kernel at the centre of each, sometimes 

 microscopic, whose presence has set the stimulus at 

 work. After the secretion has been set going, succes- 

 sive enveloping, concentric layers have been deposited 

 and the size of the concretion has increased, until we 

 have a round, regular pearl, with all its charm. 



This kernel, the initial cause, is any little thing which 

 has passed through the superficial layer of the tegument 

 and penetrated the living tissues, carrying along with it 

 some elements of the layer, and the pearl is the result. 

 The living tissues have secreted calcareous matter as they 

 always do; then the local irritation has facilitated the 

 formation of the initial cyst; finally, the remainder has 

 been deposited, layer by layer, thickening the envelope 

 thus brought into existence. 



This object from which the first impulse comes, var- 

 ies in different cases. It may originate in the creature 

 itself, some tiny fragment which has accidentally become 

 detached from the outer part of the body, and pushed 

 inside it. It may have been introduced by the hand of 

 man, as in the case of artificial pearls. Most often, it is 

 a tiny creature, a larva of a parasitic worm, which, after 

 attaching itself in the first place to the tegument, per- 

 forates it, and passes into the nearby tisues. Then the 

 mollusc reacts in its peculiar way, struggling against 

 the intruder. Most animals, in such circumstances, 

 and when they have the power, make use of their phago- 

 cytes, their lymphatic cells, which attack the intruder 

 and gradually destroy it. The mollusc uses a different 

 method. Instead of breaking up and annihilating its 

 enemy piecemeal, it surrounds and immures it. On a 

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