140 DR. H. LYSTER JAMESON ON THE [Mar. 4, 



In one genvxs all the females are blue, thus proving that this 

 beautiful green development is probably of a comparatively- 

 recent date. M. de Niceville tells us that when seen in sunlight 

 these green specimens are gems of beauty, compared with which 

 the most brilliant of the blue species are absolutely dull. 



Among many entomologists who have been most kind in 

 lending me their insects, I must mention two in particular who 

 have passed to the great majority. The late Dr. Staudinger sent 

 me over a considerable portion of his collection of this gi-oup, 

 including all his types; whilst the late M. de Niceville (in whom 

 India has lost a most energetic and untiring observer) was good 

 enough to lend me the whole of this portion of his collection ; so 

 that these two gentlemen alone furnished me with well over two 

 thousand specimens. My warm thanks are due not only to these 

 but to many others for much kind help. 



This Memoir will be printed entire in the Society's ' Trans- 

 actions.' 



The following papers were read : — 



1. On the Origin of Pearls. 

 By H. Lystek Jameson, M.A., Ph.D. 



[Received February 7, 1902.] 

 (Plates XIV.-XVII.i and Text-figures 22-24.) 



Most theoi'ies of Pearl -production have assumed that the 

 " nucleus," whatever its origin may be, is the direct cause of 

 the secretion of a true pearl, and that the latter arises as a result 

 of the mollusc's endeavour to coat with carbonate of lime an 

 irritating body. 



I do not propose in this paper to give yet another complete 

 historical survey of the various hypotheses, dating back to the 

 time of Pliny, which have been propounded. These theories 

 have been summarized over and over again by writers on pearl- 

 formation. The more recent ones may conveniently be grouped 

 under the following heads: — That pearls are (1) concretions of 

 shell- forming fluid (Reaumur, 1717); (2) shell-substance deposited 

 around bodies or concretions of internal origin (Kiichenmeister, 

 in part, 1856 ; von Hessling, 1858 ; Pagenstecher, 1858) 

 (3) formed around an abortive or displaced ovum (Home, 1826 

 Kelaart, in part, 1857) ; (4) seci^eted to coat over a grain of sand 

 (5) the result of injuiy to or perforation of the shell ; (6) caused 

 by a parasite (Filippi and others) ; (7) formed in an ampulla in 

 the tissues (Hessling, 1858 ; Diguet, 1899). Several writers have 

 allowed the possibility of two or more of these causes. 



The origin of the " grain-of-sand " theory is veiled in obscurity. 



1 For explanation of the Plates, see p. 165. 



