12 CEYLON PEARL OYSTER REPORT. 



The totals show nearly as many pearls as mussels, and nearly twice as many pearls* 

 as parasites, but that must not be considered as a conclusion that can be generally 

 applied. The last item on the list shows how much more abundant the pearls and 

 parasites may be in one locality than in others, t In fact, we do not wish to attach 

 much weight to any of these figures given above. The point we desire to make is 

 rather that in working with these comparatively small samples each fresh examination 

 gives a somewhat different result, and that, consequently, it is necessary that some 

 one living on the .spot, with abundance of material at hand and with tanks for 

 experiments under constant observation, should make a comprehensive investigation 

 of some hundreds or thousands of each kind of mussel and cockle in order to clear up 

 the distribution of pearls and parasites, and settle this question of infection. 



It must not be supposed that we are disputing Dr. Lyster Jameson's theory 

 of pearl-formation. We recognise the excellence of his work and appreciate the 

 energy he displayed in prosecuting the research, both at Billiers and at Piel. His 

 paper marks a distinct advance in our knowledge of the subject. But there remain 

 the two points on which it seems to lis the evidence in Jameson's paper is not 

 completely satisfying. These are (l) the origin of the epithelial sac that secretes 

 the pearl, and (2) the infection of the mussel from a previous molluscan host, the 

 Tapes or the cockle. There may be such a host, but Jameson's observations and 

 our own later ones leave the matter still doubtful. 



Finally we desire to emphasise the point that Jameson's observations and 

 conclusions refer to pearl-formation in the common marine mussel of North-west 

 Europe, Mytilus edulis, and cannot, without further evidence, be extended to 

 other pearl-bearing molluscs. It is becoming clear that several parasitic worms 

 and several distinct processes are at work in bringing about the production of 

 pearls in shell-fish. 



Artificial Infection. 



To continue our historical survey, Professor MTntoshJ has described the 

 examination of 700 mussels from near St. Andrews, where he found that 300 in 

 all, or nearly 43 per cent., were pearl-bearers a small proportion, however, com- 



* In comparing these statistics with those of the Ceylon pearl oyster, one is struck by the wholly 

 different ratio borne by pearls to parasites in the two cases. In the mussels, pearls are far more numerous 

 than the living parasites. In our Ceylon oyster, parasites may be exceedingly abundant ; while pearls 

 (cyst-pearls) are relatively very rare, probably not more than one to a hundred parasites. 



t Mussels that grow rapidly and regularly have few pearls. It is the old "blue-nebs" of uncertain age 

 and battered appearance that have the most pearls. We may add that the same general principle holds 

 g 1 in the case of the Ceylon pearl oyster. The most prolific pearl-bearers are those of stunted appear- 

 ance and somewhat rounded form the " Koddapakku " or Areca-nut oysters, as the divers call them. 



J 'Ann. Mag. Nat. Hist.,' June, 1903, p. 541). W. NlCOLL has a recent note ('Ann. and Mag.,' January, 

 1906) mi Trematode parasites in the cockle and mussel at St. Andrews. lie finds the adult in the oyster- 

 catcher, but it is evidently not the form described by Jameson, since Nicoll refers to it as probably a 

 new species of Echinostomum. 



