278 



the light emitted by the lime, but that none of the rays are entirely 

 wanting. No black lines crossing the spectrum could be observed. 

 He explains the cause of the peculiar coloured shadows thrown by 

 this light, as compared with those of oil and day-light ; and adds, 

 that it is remarkable that the spectrum thus emitted by incandescent 

 quicklime differs from that of the salts of lime, the characteristic 

 colour in the latter case being thick red. 



On the Production and Formation of Pearls. By Sir Everard Home, 

 Bart. V.P.R.S. Read May 11, 1826. [Phil. Trans. 1826, p. 338.] 



In his examinations of the organs of generation of the large fresh, 

 water muscle, the author often met with seed pearls, either in the 

 ovarium, or connected with the shell upon which the ovarium lay ; 

 and he remarked at the same time that all Oriental pearls have a 

 brilliant central cell, which in the common mode of boring them is 

 destroyed, but which may be beautifully exhibited by carefully split- 

 ting the pearl into halves : this cell is just large enough to contain 

 an ovum, which is formed upon a pedicle like the yolk of the pullet's 

 egg, and is similarly discharged when completely formed. Thence 

 Sir Everard concludes, that a pearl is formed upon the external sur- 

 face 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 pearl at the 

 same time that the inner surface of the shell receives its annual 

 supply. This conclusion, he observes, is verified by some pearls 

 being spherical while others are pyramidal, in consequence of the 

 pedicle, as well as the ovum, having been enamelled with nacre. 



This paper concludes with an extract from one of the early volumes 

 of the Philosophical Transactions, in which a corresponding account 

 of the growth of pearls is announced by Arnoldi in 1673. 



On Burrowing and Boring Marine Animals. By Edward Osier, Esq. 

 Communicated February 15, 1826, by L. W. Dillwyn, Esq. F.R.S. 

 Read May 25, 1826. [Phil. Trans. 1826, p. 342.] 



The author's object in this paper is to describe the mechanism by 

 which the boring and burrowing shell-fish form their habitations, 

 and to explain some parts respecting the burrowing of other marine 

 animals. 



After showing that the Nereides bury themselves by the undu- 

 lating motion which they employ in swimming, aided by the action 

 of their bristly feet, and that the Arenicola piscatorum forms its im- 

 perfect arenaceous tube by the aid of a viscid secretion which exudes 

 from the anterior half of the animal, he particularly describes the 

 habits of the Tercbella conchileoa, showing that by a glutinous se- 

 cretion it cements together particles of shells and sand, so as to form 

 a collar, which is regularly and curiously lengthened into a tube ; 

 and when this is about an inch in length the animal proceeds to 



