THE CRYLOX PEAUL-OYSTER. 349 



from the blood " (Southwell), but are minute peai'Is formed 

 of the hypostracum or muscle-attachment substance. They are 

 therefore not the cause of the nacreous muscle-pearls, but a phase 

 parallel to them. There is some reason to believe that the origin 

 of muscle-pearls is associated with pathological invaginations 

 or immigrations of the epidermis at the points where the 

 muscle-attachment epithelium passes over into the ordinary 

 outer mantle-epithelium. 



(5) Parenchyma-pearls (which name I apply to Prof. Herdman's 

 cyst-pearls) may be formed around grains of sand or other foreign 

 particles, organic granular matter of doubtful origin, or bodies 

 composed of varieties of the shell-substance which arise when 

 the normal rhythm of secretion is disturbed (repair-substance). 

 A foreign nucleus is probably rather exceptional. The ultimate 

 factors which give rise to the epidermal sacs in which they are 

 formed have yet to be discovered. Many of them are probably 

 of the same origin as muscle-pearls, except that they arise singly 

 at points where a few muscle-fibres are inserted into the shell, 

 instead of in clusters at the regular muscle-insertions. The 

 dark pseudo-nuclei of these pearls, which may easily be mistaken 

 for the remains of parasites, are usually composed of the repair- 

 substances. 



(16) Works referred to. 



(1) BiEDEEMANN, W. 1901. — Untersucliuiigen iiber Bau und Entsteliung der 



Molhiskenschalen. Jenaische Zeitschr. f. Naturwiss. Bd. xxxvi. Hft i 

 pp. 1-164, Taf. i.-vi. 1901. 



(2) BiEDERMANN, W. 1902.— Ueber die Bedeutung voii Kri'stallisationspi-ozesseu 



bei der Bildung der Skelette wirbelloser Thiere, naiiK'ntlich dur iMol- 

 lusken. Zoitschr. f. allg. Physiologie, Bd. i. pp. 154.-208. Jena, lOO'J. 



(3) BouTAN, L. 1903.— L'origine reelle des Perles tines. C.R. Acad. Sci., Dec. 11, 



1903, t. cxxxvii. p. lo73. 



(4) BouTAN, L. 1904.— Les Perles fines, leur Origine reelle. Arch. Zool. Exper., 



Ser. 4, t. ii. pp. 47-90. 1904. 



(5) BiiTSCHLi, O. 1898.— Untersucliungen iiber Strukturen. Leipzig, 1898. 



(6) BiJiscHLi, 0. 1908.— Untersuchungen uber organische Kalkgebilde. Abhandl. 



d. konigl. Gesellsch. der Wissenschaften zu Gottingen, Math.-Pliys. 

 Klasse, Neue Folge, Bd. vi. no. 3. 1908. 



(7) Dubois, R. 1907. — Sur nn Sporozoaire parasite de rHuitreperliere(ilfar^rtr/- 



tifera vulgaris). Son Bole dans la Formation des Perles tines. C.K. 

 Soc. Biol. Ixii. 1907, pp. 310-312. , 



(8) Dubois, K. 1909.— Contribution a I'Etude des Perles lines. Annales dc 



rUniversite de Lyon, n. s., i. Sciences — Medicine, Fascicule 29. 1909. 



(9) Eheenbaum, K. 1885.— Untersuchungen iiber die Struktur und Bildung 



der Schale der in der Kieler Bucht hiiufig vorkomnienden Muscheh". 

 Zeitschr. f. wiss. Zool. Bd. xli. 1885, pp. 1-46, Taf. i.-ii. 



(10) GiAED, A. 1903. — L'origine Parasitaire des Perles d'apres les recherches de 



M. G. Seurat. Comptes-rendus des S<5ances de la Societe de Biologie 

 (Seance du 31 Octobre, 1903), t. Iv. p. 1222. 1903. 



(11) Haeiey, G. 1889.— The Structural Arrangement of the Mineral Matters in 



Sedimentary and Crystalline Pearls. Proc. Roy. Soc. vol. xlv. no 279 

 pp. 612-614. 



(12) Haeting, p. 1872.— Recherches de morphologic .synthetique sur la production 



artificielle de quelques formations calcaires organiques. Verhandl. d. 

 Kon. Akad. d. Vetenskapp. Amsterdam, Deel 14, 1872, 85 pp., 4 pis. 



(13) Hekdman, W. a. 1902.— Reports on the Pearl Fisheries of Ceylon. 



Preliminary Report. Ceylon Sessional Papers, xii. 1902. 



(14) IIERUMA^f, W. A. 1903.— Lecture delivered at the Royal Institution (m 



March 27th, 1903; Abstract in 'Nature,' vol. 67, 1903, pp. 620-622. 



