WHAT IS A PEARL? 281 



reared as articles of food, it is worth while to consider 

 whether the bivalved molluscs producing pearls may 

 also become the subjects of improved culture. As there 

 is evidence that they may, we think it may interest some 

 of our readers to make them acquainted with it. 



But we have first to consider the vexed question, 

 What is a pearl ? According to an old popular fancy, 

 pearls are dew-drops, which are transmogrified thus, 

 according to Boethius : " Early in the morning, the 

 mussels, in the gentle, cleare, and calme aire, lift up 

 their upper shells and mouthes above the water, and 

 these receive of the fine and pleasant breath or dew of 

 heaven ; and afterwards, according to the measure and 

 quantitie of this vitall force received, they first con- 

 ceive, then swell, and finallie produce the pearle." 

 Poets having taken up this fancy, it survived until the 

 researches of Mr Gray and Sir Everard Home demon- 

 strated that pearls are merely the internal pearly coat 

 of the shell, which, from some extraneous cause, has 

 assumed a spherical form. It is supposed that the shell 

 of the mollusc having been penetrated by one of its 

 enemies, the creature repels the invader by the secre- 

 tion of nacre ; or, where sand or other small bodies 

 have been accidentally introduced, they are covered 

 with nacre as a protection against the irritation caused 

 by their presence. A pearl having been once formed, 

 the animal continues depositing concentric layers of 

 fresh nacre. The pearls are usually of the colour of 

 the part of the shell to which they are attached. " I 

 have observed them," says Mr Gray, " white, rose- 

 coloured, purple, and black, and they are sometimes 

 said to be of a green colour. Their lustre, which is 

 derived from the reflection of the light from their pecu- 

 liar surface, produced by the curious disposition of their 

 fibres, and from their semi-transparency and form, greatly 

 depends on the uniformity of their texture and colour of 

 the concentric coats of which they are formed." * 

 * ' Annals of Philosophy,' 1824. 



