their Secretions, 617 



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, having 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 py- 

 ramidal form, from the pedicle having received a coat of nacre 

 as well as the ovum." (Phil. Tra7is., 18^26, partiii. p. 839.) 



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 becomes 

 extended over them and the margin, gives them that appear- 

 ance. 



" Pearls vary greatly in their transparency. The pink are 

 the most transparent; and in this particular they agree with 

 the internal coat of the shell from which they are formed ; for 

 these pearls are only formed on the Pinnae, which internally 

 are pink and semitransparent, and the black and purple spe- 

 cimens are generally more or less opaque. 



" Their lustre, which is derived from the reflection of the 



* " There are, besides, (in Britain,) several sorts of shellfish, among 

 which are muscles, containing pearls often of the best kind, and of every 

 colour ; that is, red, purple, violet, green (prasini), but principally white, 

 as we find in the Venerable Bede's Ecclesiastical Histo?y." (Richard of 

 Cirencestei^ transl. p. 28.) Philosophy has destroyed many a fine hypo- 

 thesis, as witnesses the following, explanatory of the variations in colour 

 of these bodies : — 



" With open shells in seas, on heavenly dew, 

 A shining oyster lusciously doth feed ; 

 And then the birth of that ethereal seed 

 Shows, when conceived, if skies look dark or blue ; 

 Pearls, then, are orient-framed, and fair in form, 

 If heavens in their conception do look clear ; 

 But if they thunder, or do threat a storm. 



They sadly dark and cloudy do appear." Drummond. 



(Note hy G. J.) 



