616 Natural History of Molluscous Ariimals : — 



throwing into its shell, when open, five or six minute mother- 

 of-pearl beads strung on a thread : in the course of one year, 

 these are found covered with a crust which perfectly resembles 

 the real pearl.* The extraneous body which naturally serves 

 for the nucleus, appears to be very often, or, as Sir E. Home 

 says, always, a blighted ovum. Christophorus Sandius, in 

 1673, on the authority of Henricus Arnoldi, " an ingenious 

 and veracious person," asserted that the ova left unexpelled 

 from the shell became the nuclei on which pearls, in the 

 freshwater muscle, were formed. " Sometimes,'' he Says, " it 

 happens that one or two of these eggs stick fast to the sides 

 of the matrix, and are not voided with the rest. These are 

 fed by the oyster against her will ; and they do grow, accord- 

 ing to the length of time, into pearls of sufficient bigness, 

 and imprint a mark both on the fish and the shell, by the 

 situation, conform to its figure." This theory has been fully 

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

 above quotation. " If," says the enthusiastic baronet, " I 

 shall prove that this, the richest jewel in a monarch'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 enve- 

 loped 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 ?" (Comp, Anat,^ vol. v. 

 p. 302.) And, as proofs of this, he informs us that he has 

 always found the seed pearls in the ovarium, or connected 



* The Chinese appear to have more ways than one of getting artificial 

 pearls. Sir E. Home says their method is this : — " They take the sub- 

 stance of the clamp-shell, turn it in a lathe into hemispheres of different 

 sizes, and introduce them through the shell of the oyster, with the convex 

 surface towards the animal ; the prominent part is, consequently, covered 

 with nacre, and annually receives an increase. By introducing hemispheres 

 instead of spheres, they avoid irregularities on the opposite surface. In 

 this manner half pearls are made, since they cannot make whole ones ; and 

 when these are set to represent pearls, they will pass off undiscovered by an 

 unexperienced eye, but not by those who understand pearls, being deficient 

 in lustre." {Comp. Anat.y vol. v. p. 296.) Mr. Gray, however, has proved 

 that this people introduce, for the same purpose, pieces of mother-of-pearl 

 " between the leaf of the mantle and the internal coat of the shell ; for 

 they could not have been put in through a hole in the shell, as there was 

 not the slightest appearance of any injury near the situation of the pearls 

 on the outer coat." Mr. Gray tried the experiment on our freshwater 

 muscles, by introducing pieces of mother-of-pearl between the mantle and 

 the shell ; but with the result I am not acquainted. He adds : — " If this 

 plan succeed, which I have scarcely any doubt it will, we shall be able to 

 produce any quantity of as fine pearls as can be procured from abroad.*' 

 (Ho)ne's Lectures, vol. v. p. 300,301.) The original paper is in the Annals 

 of Fhihso'phy , for, I believe, January, 1825. 



