the Pearl Oyster and on the Production of Pearls. 97 



of pearly asperities, of various forms and development, passing 

 through all possible degrees to real, shining, nearly spherical pearls, 

 scattered over the adjacent surface of the shell." On carefully 

 removing the pearly concretions which appeared to be youngest, 

 and examining them with the microscope, he always detected in 

 them the remains of Distomata {Cercarice), which had served as 

 the nucleus for the calcareous matter. Even in free pearls he 

 found an organic nucleus (consisting of portions of Echino- 

 stomum and Limnochares Anodonta), although he never found 

 any animal that could be determined with perfect certainty. 

 From these observations Filippi concludes that the production 

 of pearls is intimately connected with the presence of parasites, 

 and that the want of the latter may be the cause of the non- 

 formation of pearls in some localities. He denies that pearls 

 are the result of disease, and that their nuclei are ever formed 

 by grains of sand. 



Kiichenmeister*, following up the ideas of Filippi, and admit- 

 ting that pearls may be produced by the intrusion of Distoma- 

 larvse and other Entozoa into the mantle, maintains that the 

 principal impulse to the formation of pearls, at all events in the 

 Saxon river Elster, is given by the water-mite Limnochares Ano- 

 donta. The eggs of this mite are deposited in the fresh-water 

 mussels, and enveloped by the latter in cysts, from which, how- 

 ever, the six-legged young can usually escape with ease. After 

 swimming about for some time, and attaining their full growth 

 as larvae, these hexapod mites return into the mollusk, and be- 

 come again enclosed in a capsule, within which they change 

 their skin and acquire their perfect form. Thus the natural 

 habits of this mite give rise to the formation of numerous sphe- 

 rical cysts, which may remain in the mantle of the mollusk even 

 after the escape of their inmates, and thus furnish the most 

 favourable conditions for the production of rounded pearls. The 

 mites prefer still water, and it is in situations where this condi- 

 tion is fulfilled that the greatest number of pearls are found. 



Kiichenmeister's observations induced Von Hessling to in- 

 vestigate this interesting subject in the Bavarian waters, and the 

 results of his researches were published in the Gelehrten Anzeigen 

 of Munich (1856). In adherent pearly asperities of the inner 

 surface of the shells of fresh-water mussels he found ^' partly 

 true sand-grains, or minute particles of fine mud, in which the 

 animals live; partly remains of Algse with distinctly recogniza- 

 ble conjugations, the individual cellular segments of which are 

 still incrusted ; partly eggs in the most various stages of deve- 

 lopment and decomposition ; and partly parasitic animals in the 

 most various stages of development." He only found one Di- 

 * Miiller's Archiv, 1856, p. 269. 



Ann, ^ Mag. N, Hist, Ser. 3. Vol.'i. 7 



