1902.] ORIGIX OF PEARLS. 165 



1885. MiJLLER, Felix. — Uber die Schalenbildung bei Lamelli- 



branchiaten. Schneider's Zool. Beitrage, Bd. i. S. 206- 



246, Taf. xxviii.-xxx. 1885. 

 1892. MoYXiER DE ViLLEPOix. — Reclierches sur la Fomaation et 



rAccroissement de la Coquille des MoUusques. Joum. de 



I'Anat. et de la Physiol, xxviii. pp. 461-518, pLs. 19, 20. 



1892. 

 1894. d'Hamoxville, L. — Les Moules perlieres de Billiers. Bull. 



Soc. Zool. France, 1894, pp. 140-142. 

 1894. Thurston, E.— Pearl and Chank Fisheries of the Gulf of 



Manaar. Madras Govt. Museum, Bull. No. 1. Madras, 



1894. 

 1896. Loos. — Recherches siu' la Faune parasitaire de I'Egypte, 



Cairo, 1896. 

 1898. OoMBA, B.— La Madreperla. Torino, 1898. 



1898. vox Nathusius-Koxigsborx, W. — Uber die Gestaltungs- 



ursachen der Haare, der Eischalen, der Mollusken- 

 schalen und der Haiting'schen Korperchen. Archiv f. 

 Entwickelungsmechanik, vi. pp. ,365-39.3. 1898. 



1899. Stossich, M. — Lo smembramento dei Brachycoelium. 



Trieste, 1899. 

 1899. Diguet, L. — Sur la Formation de la Perle fine chez la 



Meleagrina margaritifera. 0. R. Acad. Sci. Paris, 



cxxviii. pp. 1589-1591. 

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Mother-of- Pearl Oysters. P. Z. S. 1901, vol. i. pp. 372- 



394. 

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stehung der Molluskenschalen. Jenaische Zeitschr. f. 



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fines dans le Mytilus edulis. O.R. Acad. Sci. Paris 



cxxxiii. pp. 603-605. 



EXPLANATION OF THE PLATES. 

 Plate XIV. 



Mytilus edulis. 



Fig. 1. Mytilus edulis L., Billiers. Section of a small Pearl, decalcified in situ, 

 showing remains of Trematode as nucleus, ext.ep., external epidermis of 

 mantle; c.t., connective tissue; hi., blood-corpuscles; s., epithelium of 

 pearl-sac; con., conchyolin basis of pearl; con.', outermost uncalcilied 

 layer of same, attached to epithelium ; cti,., cuticle of dead Trematode ; ph., 

 pharynx, and dig., digestive system of same. X 90. 



Fig. 2. The Trematode larva in the connective tissue of the mantle, prior to foiina- 

 tion of sac. f., fibres of connective tissue ; pr., proliferating cells which 

 give rise to the epithelial sac ; cu., cuticle ; dig., digestive csca ; ex., excre- 

 tory organs, and pa., parenchj'ma of the parasite. Other figures as above. 

 X 130. The section passes between pharjuix and ventral sucker. The 

 ventral surface of the parasite is turned towards external epidermis. 



Fig. 3. The cells of the proliferating epithelium which is destined to become the 

 sac {cf. fig. 12). nu., nuclei with chromatine reticulum ; c.t., connective 

 tissue. 



Fig. 4. Cells of the fully-formed sac which surrounds the Cercaria in fig. 2. c.t., 

 underlying connective-tissue cells and fibres. 



