THE CEYLON PEARL-OYSTER. 349 
from the blood” (Southwell), but are minute pearls 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) Brepermany, W. 1901.—Untersuchungen tiber Bau und Entstebung der 
Molluskenschalen. Jenaische Zeitschr. f. Naturwiss. Bd. xxxvi. Hft. i. 
pp. 1-164, Taf. i-vi. 1901. 
(2) Brepermann, W. 1902.—Ueber die Bedeutung von Krystallisationsprozessen 
bei der Bildung der Skelette wirbelloser Thiere, namentlich der Mol- 
lusken. Zeitschr. f. allg. Physiologie, Bd. i. pp. 154-208. Jena, 1902. 
(3) Bouran, L. 1903.—L’origine réelle des Perles fines. C.R. Acad. Sci., Dec. 14, 
1903, t. exxxvil. p. 1073. 
(4) Bouran, L. 1904.—Les Perles fines, leur Origine réelle. Arch. Zool. Expér., 
Sér. 4, t. ii. pp. 47-90. 1904. 
(5) Buirscutr, O. 1898.—Untersuchungen tiber Strukturen. Leipzig, 1898. 
(6) Birscrtt, O. 1908.—Untersuchungen tiber organische Kalkgebilde. Abhandl. 
d. konigl. Gesellsch. der Wissenschaften zu Géttingen, Math.-Phys. 
Klasse, Neue Folge, Bd. vi.no. 3. 1908. 
(7) Dusors, R. 1907.—Sur un Sporozoaire parasite de ! Huitre perliére (Margari- 
tifera vulgaris). Son Réle dans la Formation des Perles fines. C.R. 
Soe. Biol. lxii. 1907, pp. 310-312. _ 
(8) Dusors, R. 1909.—Contribution a ?Etude des Perles fines. Annales de 
VUniversité de Lyon, n. s., i. Sciences—Médicine, Fascicule 29. 1909. 
(9) Enrenpaum, EK. 1885.—Untersuchungen tiber die Struktur und Bildung 
der Schale der in der Kieler Bucht haufig vorkommenden Muscheln. 
Zeitschr. f. wiss. Zool. Bd. xli. 1885, pp. 1-46, Taf. iii. 
(10) Gtarp, A. 1903.—L’origine Parasitaire des Perles d’aprés les recherches de 
M. G. Seurat. Comptes-rendus des Séances de la Société de Biologie 
(Séance du 31 Octobre, 1903), t. lv. p. 1222. 1903. 
(11) Hartey, 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) Harine, P. 1872.—Recherches de morphologie synthétique sur la production 
artificielle de quelques formations calcaires organiques. Verhandl. d. 
Kon. Akad. d. Vetenskapp. Amsterdam, Deel 14, 1872, 85 pp., 4 pls. 
(13). Herpman, W. A. 1902.—Reports on the Pearl Fisheries of Ceylon. 
Preliminary Report. Ceylon Sessional Papers, xii. 1902. 
(14) Herpman, W. A. 1903.—Lecture delivered at the Royal Institution on 
March 27th, 1903; Abstract in ‘ Nature,’ vol. 67, 1903, pp. 620-622. 
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