1902.] ORIGIN OF PEARLS. 141 



It has had many supporters, and still maintains a prominent 

 position in zoological text-books and popidar compilations. It is 

 doubtless largely due to a confusion of true pearls with "blisters " 

 or pearly excrescences on the shell. There is no recorded instance 

 of an undoubted sand-grain having been found in a pearl, 

 although hundi-eds have been examined. All attempts to produce 

 pearls by introducing such bodies into the tissues or between the 

 shell and mantle have led, at best, only to the formation of 

 " blistei's." Such methods of obtaining the latter have long been 

 known to the Chinese, and have repeatedly been applied in other 

 countries. Chemnitz, Beckmann, and others (1791) regarded 

 Linnfeus's " secret process " as mei-ely boring the shells. However, 

 no subseqvient boiing experiments have yielded anything but 

 blisters, and the popular notion of Linnseus's Tnodus operandi is 

 little more than a guess. A great step in the right dii-ection was 

 made when Filippi, in 1852, discovered the connection between 

 pearls and the presence of Distonnum duplicatum in Anodonta. 

 Filippi regarded these Trematodes as encysted. In his later 

 papers he allowed other forms such as Atax ypsilophorus to be 

 occasional causes of pearl -formation. He recognized that the 

 action of these parasites was specific, and compared it to the 

 formation of plant-galls. Kiichenmeister (1856) associated pearls 

 in Margaritana margaritifera with the larvae of Atax ypsilo- 

 phorus van Beneden, which occur in the mantle, enclosed in cysts 

 secreted by the mollusc. He held that other pai-asites, as well 

 as bodies of internal origin, might also cause pearls. 



Mobius (1857) found Trematode remains in pearls from the 

 Pearl-Oyster of the West Coast of America (probably Margaritifera 

 margaritifera L., var. mazatlanica Hanley ^). Kelaart (1859) 

 held that parasites played an important part in pearl- formation 

 in Margaritifera vulgaris (Schumacher) in Ceylon, but did not 

 associate any definite organism with it, although he found several 

 species living in the Pearl-Oyster. Thurston (1894) confirmed 

 the existence of platyhelminthan parasites in the same species, 

 biit did not assert that they had anything to do with pearl- 

 production. Garner (1871) found that pearls in Mytilus edulis 

 and Margaritana margaritifera were due to Distomids, against 

 which the molluscs protected themselves by coating them with 

 calcium-carbonate. Comba (1898), who claims to have discovered 

 a method of producing free pearls by ai-tificial means, says (p. 6) 

 that the cause is " un parassito il quale viene dal mollusco awi- 

 luppato di strati di una bava che indurendosi foi-ma la perla 

 formando cosi una pustola ed una pallina che ci-esce in grossezza." 



Dubois (1901) found in Mytilus edulis that the production of 

 pearls was due to Distomid larvfe, to which (without description) 

 he applied the name Disfomum margaritarum. His account of 

 the " desagregation " of formed pearls, and the liberation, to repeat 

 their life-cycle, of the parasites that form their nuclei, is quite at 



1 For revised nomenclature of the Pearl-Oysters, see Jameson, 1901. 



