260 DK. n. LYSTER JAMESON ON 



18. Studies on Pearl-Ojsters and Pearls. — I. The Structure 

 of the Shell and Pearls of the Oeylon Pearl-Ojster 

 (Margaritifh'a vulgaris Schumacher) : with an Exami- 

 nation of the Cestode Theory of Pearl-Production. By 

 H. Lyster Jameson, M.A., D.Sc, Ph D., F.Z.S. 



[Received November 20, 1911 : Read February 20, 1912.] 

 (Plates XXXIII.-XLYII. and Text-figures 33-41.) 



Contents. p,^^^ 



(1) Introduction 260 



(2) Outline of the recent Investigations in Ceylon • 262 



(3) Professor Herdman's Conclusions on Pearl-Formation 265 



(4) PZxamination of the Cestode Theory of Pearl-Production 271 



(5) Description of the two Globular Cestode Larv<e from the Ceylon Pearl- 



Oyster 290 



(6) Observations on the Structure of the Fibrous Cysts surrounding the 



Cestode Larva; in 3Iargaritifera vulgaris 293 



(7) Materials available for the Present Investigations 294 



(8) Methods 299 



(9) Structure of the Shell-Substances 299 



(10) The Shell-secreting Epithelia 307 



(11) Shell-Secretion 308 



(12) Abnormal and Pathological Phases of the Shell-Substance 310 



(13) Varieties of Ceylon Pearls 319 



A. Muscle-Pearls 321 



B. Parenchyma-Pearls (" Cyst-Pearls," Herdman) 330 



(14) Descriptions of the Centres of Individual Pearls 331 



A. Material from the Persian Gulf 331 



B. Pearls purchased in Cejdon 332 



C. Professor Herdman's Slides 336 



D. Unlabelled Pearls (dry) in the British Museum 337 



E. Collection of Pearls given to me by Mr. Max Mayer 338 



F. Collection of Ceylon Pearls given to me by Mr. E. 



Hopkins 339 



G. Pearls from Margaritifera vulgaris froni the Gulf of Kutch . . . 341 

 H. Pearls from M. vulgaris from the Mediterranean 343 



I. Pearls from 31. vulgaris from New Caledonia 343 



J. Pearl from M. vulgaris from Nossi-B^, Madagascar 344 



K. Pearls from the Lapi shell {M. vulgaris) from the Trobriand 



Islands, Papua , 344 



L. Pearls from Flacima placenta from Lake Tampalakamam, 



Cej'lon 345 



M. Pearls from Jf. margaritifera var. cumingii Reeve (the 

 Black-edged Mother-of-Pearl Oyster) from Rikitea, Gam- 

 bier Archipelago 346 



(15) General Summary 347 



(16) Works referred to 349 



(17) Explanation of the Plates 352 



(1) Introduction. 

 The studies which are embodied in this paper have been deferred 

 and interrupted. Wlien Professor Herdman pubHshed liis Report 



