130 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



giving rise to irritation and the subsequent secretion by the animal 

 of perlaceous growths. Although this view might occasionally hold 

 good, it is distinctly proved by modern researches that the majority 

 of peaiis are dei'ived from an organic nucleus due to certain para- 

 sitical worms which infest the soft parts of the mollusc. Such 

 a discovery is by no means new, and we owe it to very early 

 investigators, going back to Rondeletius in 1558 and even before his 

 time. The more systematic work was, however, accomplished by 

 Professor Y. de Filippi^ in the early fifties, who demonstrated that 

 the Trematode parasite, Distomum duplicatum, was the cause of pearl- 

 formation in the fresh-water mussel Anodonta. Kiichenmeister,^ 

 working on the same lines, extended this view to other pearl-pro- 

 ducing shells and to other parasites, and he found that peaiis were 

 most abundant in the quiet waters of the Eiver Elster, Saxony, where 

 water-mites {Limnochares anodontce) existed most numerously. In 

 1857 Kelaart^ investigated the natural history of Margaritifera vulgaris, 

 the pearl-oyster of Ceylon, and was probably the first to prove the 

 presence of parasitical worms in the soft parts of that animal, to which 

 he traced the origin of the pearl concretions. "Without quoting the 

 later writers on this subject, it is enough to refer the student to 

 Professor Herdman's comprehensive " E,eport to the Government of 

 Ceylon on the Pearl Oyster Fisheries of the Gulf of Manaar," 

 published in five volumes by the Royal Society between the years 

 1903 and 1906. For this work Messrs. A. E. Shipley and James 

 Hornell have contributed a most valuable memoir on " The Parasites 

 of the Pearl Oyster," which are regarded by them as belonging to 

 three groups of the Entozoa, viz. Cestodes, Trematodes, and Nema- 

 todes (1904, vol. iv, pp. 77-106, pis. i-iv), whilst Professor Herdman, 

 in conjunction with Mr. J. Hornell, has written a special chapter on 

 " Pearl Production," which is of the highest importance (1906, vol. v, 

 pp. 1-42, pis. i-iii). 



According to Dr. H. Lyster Jameson,* the term ' blisters ' is applied 

 to "internal excrescences of the shell, caused by the intrusion of 

 foreign bodies between the mantle and the shell, or by the secretion 

 of a nacreous cicatrix to close the perforations of boring molluscs, 

 worms, or sponges. These are sometimes referred to as ' attached 

 pearls,' or even as * pearls,' but have a totally different mode of 

 origin, and should never be confused with the latter." Valves of 

 Mytilus edulis are sometimes furnished with the so-called 'blisters,' 

 which may have been produced in the manner indicated, as minute 

 perforations are observable on the external surface of some examples 

 in the zoological department of the British Museum. 



1 " Sull' origine delle Perle " : II Cimento (Torino), 1852, vol. i, pp. 429-37. 



This paper was translated by Kiichenmeister in Miiller's Archiv Anat. Physiol. , 

 1856, pp. 251-68. 



2 Miiller's Archiv Anat. Physiol., 1856, pp. 269-81. 



3 " Introductory Report on the Natural History of the Pearl Oyster of Ceylon" : 



reviewed by J. S. Dallas in the Ann. Mag. Nat. Hist., 1858, vol. i, pp. 81-100. 

 * " On the Origin of Pearls " : Proc. Zool. Soc. London, 1902, vol. i, p. 147. 



