40 CEYLON PEARL OYSTER REPORT. 



EXPLANATION OF THE PLATES. 

 PLATE I. 



Fig. 1. Part of a gill lamella of Mytilus edulis, showing a larger pearl occupying the whole thickness of 



the lamella and a smaller one in an enlarged gill filament, x 40. 



2. Group of four pearls in the mantle of Mytilus edulis two of the pearls being in one sac. x 40. 

 3. Pearl from the mantle of Mytilus edulis, showing a small, but quite simple nucleus, evidently, 



from its staining, an organic particle, but having no visible structure, x 40. 

 4. Pearl from the mantle of Mytilus edulis, showing a relatively very large, deeply stained, but 



disorganised nucleus, x 40. 

 5. Pearl from the mantle of Mytilus edulis, showing no nucleus, no cavities, and no foreign 



structure, x 100. 



6. Pearl and Trematode lying together in the mantle of Mytilus edulis. x 40. 

 7. Pearl (with several centres) and Trematode lying together, enclosed in the same sac, in the 



mantle of Mytilus edulis. x 40. 

 ,, 8. Pearl in a gill lamella of Mytilus edulis, showing a very large, disorganised nucleus, and a 



distinct sac, with epithelium closely resembling that of the adjacent ectoderm, x 300. 

 9. Pearl from Mytilus edulis, decalcified to show the layers of conchiolin. x 40. 

 10. Portion of a pearl and its sac (p.s.) from the mantle of Mytilus edulis, to show the similarity 



between the epithelium and the ectoderm (Ed.}, x 300. 

 11. Another portion of a pearl and its epithelial sac from the mantle of Mytilus edulis, to show 



irregularly projecting parts of the pearl cut separately, x 300. 



12. Adjacent portions of pearl sac and ectoderm from fig. 10, to show similarity, x 1000. 

 ,, 13. Section through a Ceylon pearl in the natural condition, x 40. 

 14. A partially decalcified pearl in the mantle of the Ceylon pearl oyster, x 100. 

 15. Section through a partially decalcified Ceylon pearl, x 100. 



16. Portion of pearl sac and adjacent ectoderm of Ceylon pearl, to show similarity, x 1000. 

 17. Portion of a Ceylon pearl and its epithelial sac. x 200. 



18. Portion of Ceylon pearl and its epithelial sac and mantle, to show large clear cells, x 900. 

 19. Ceylon pearl and mantle, to show the large clear cells in the ectoderm (B) and in the pearl 



sac (A), x 900. 



20. Mantle of Ceylon pearl oyster over a pearl, to show the distribution of the large clear cells. 

 x900. 



PLATE II. 



Fig. 1. Margin of mantle of a highly infected Ceylon pearl oyster from Muttuvaratu Paar, showing nine 



encysted Cestode larvae. Natural size. 

 2. Transverse section through viscera of Ceylon pearl oyster, showing four Cestode cysts in the 



liver. Slightly enlarged. 



3. Gill filaments of Ceylon pearl oyster, showing encysted Cestode larva, x 12. 

 4. A. Outline of a cyst pearl for comparison with B, Outline of the Cestode larva that forms the 



pearl-nucleus, x 20. 



