268 THE NATURAL HISTORY OF 



fully adopted by Sir E. Home, from whose paper I have 

 made the above quotation. ' If,' says the enthusiastic Ba- 

 ronet, ' I shall prove that this, the richest jewel in a mo- 

 narch's crown, which cannot be imitated by any art of man, 

 either in the beauty of its form or the brilliancy and lustre 

 produced by a central illuminated cell, is the abortive egg 

 of an oyster enveloped in its own nacre, of which it receives 

 annually a layer of increase during the life of the animal, 

 who will not be struck with wonder and astonishment? * And, 

 as proofs of this, he informs us that he has always found the 

 aeed-pearls in the ovarium, or connected with that part of the 

 shell on which the ovarium lay ; and he has discovered that 

 all Oriental pearls have a brilliant cell in the centre, of a 

 size exactly large enough to contain one of the ova. ' From 

 these facts, I have been led to conclude that a pearl is 

 formed upon the external surface of an ovum ; which, hav- 

 ing been blighted, does not pass with the others into the 

 oviduct, but remains attached to its pedicle in the ovarium, 

 and, in the following season, receives a coat of nacre at the 

 same time that the internal surface of the shell receives its 

 annual supply. ' This conclusion,' he adds, < is verified by 

 some pearls being spherical ; others having a pyramidal form, 

 from the pedicle having received a coat of nacre as well as 

 the ovum.'f 



"I will conclude what I have to say concerning pearls 

 with the following extract from the paper of Mr. Gray, 

 quoted in the preceding page : — * The pearls are usually of 

 the colour of the part of the shell to which they are attached. 

 I have observed them white, rose-coloured, purple, and 

 black ; and they are said to be sometimes of a green colour. 

 They have also been found of two colours ; that is, white 

 with a dark nucleus, which is occasioned by their being first 

 formed on the dark margin of the shell before it is covered 

 with the white and pearly coat of the disk, which, when it 



* Sir Everard Home, vol. v. p. 302. 



t Philosophical Transactions, 1816. Part iii. p. 339. 



