PEARL PRODUCTION. 



the history of this inquiry, with, where known, the species of shell-fish on which the 

 ohservations were made, and an indication of the view held, with more or less 

 justification, as to the nature of the nucleus around which the pearl is formed. 



Author. 



Shell-fish investigated. 



View as to origin of pearl or nature 

 of nucleus. 



ANDROSTHENES 

 PLINY 



RONDELETIUS, 1554 . 

 REDI, 1671 .... 

 REAUMUR, 1717 . . . 

 BOHADSCH, 1761 . . 

 Sir E. HOME, 1826 . . 

 FILIPPI, 1852-56 . . 

 KUCHENMEISTER, 1856 

 VON HESSLING, 1856 . 

 MECKEL, 1856 . . . 

 MOEBIUS, 1857 . . . 

 KELAART, 1857-59 . . 

 PAGENSTECHER, 1858 . 

 GARNER, 1863, 1871 . 

 HARLEY, 1889 . . . 



Oriental pearl oyster 

 Oriental pearl oyster 

 Oriental pearl oyster 



Pinna, &c 



Aplysia 



Anodonta 



Anodonta 



Margaritana and Anodonta 

 Margaritana and Anodonta 



Both marine and fresh-water 

 Ceylon pearl oyster . 



COMBA, 1898. 

 DIGUET, 1899 



GIARD, 1897, 1901 . . . . 

 DUBOIS, 1901, 1903 . . . 



JAMESON, 1902 



HERDMAN and HORNELL, 



1902, 1903, 1906 

 SEURAT and GIARD, 1903, 



1904, 1906 



SHIPLEY and HORNELL, 1904 

 CROSSLAND, 1905 . . . . 

 HORNELL, 1905 



Anodonta and Mytilus . . . . 



" British, Australian and Cey- 



lonese " oysters 



Margaritifera mdgaris . . . . 



Meleagrina margaritifera . . . 



Donax, Tellina, &c 



Mytilus and Margaritifera 



Mytilus edulis 



Ceylon pearl oyster (Margariti- 

 fera mdgaris) 

 Margaritifera margaritifera . 



Ceylon pearl oyster . . . , 

 Red Sea pearl oyster . . . , 

 PlacMna placenta 



(?) Cestodes. 



Drops of dew. 



Lightning-flash. 



Parasites ; also concretions. 



Grain of sand. 



Pathological effusion of shell-matter. 



Calculi. 



Abortive ova. 



Distomum, (Cercaria), &c. 



Mite (Limnochares anodontce). 



Sand, algae, ova, parasites. 



Calculi. 



Entozoa. 



Sand, diatoms, ova, parasites. 



Pathological concretions. 



Distomum, 



Calculi round inorganic or organic 



particles. 

 Parasites. 

 Pathological calcification of fluid formed 



around parasite. 

 Distomids. 

 Distomid larvse. 

 Distomicl (Cercaria). 

 Larval Cestodes. 



Larval Cestodes. 



Larval Cestodes. 

 Larval Cestodes. 

 Larval Cestodes, rarely Distomids. 



Omitting the more fanciful views, there are evidently three main methods which 

 have been advanced as explaining the formation of pearls ; and as is not infrequently 

 the case when there are several competing theories, it cannot be said that one only is 

 correct and of universal application and that the others are quite erroneous. The 

 three methods referred to are : (1) The grain-of-sand irritation ; (2) the pathological 

 secretion ; and (3) the stimulation caused by the presence of a parasitic worm which 

 acts as a nucleus, around which an epithelial sac deposits successive layers of pearly 

 material. We shall briefly examine each of these views in turn. 



Most of the attempts* at artificial ' : margarosis " the production of pearls by 

 stimulation of the Mollusc have been based upon the belief that the nucleus of the 



* There is, however, another artificial method which has been suggested by infection with the 

 parasites which will be discussed below. 



B 2 



