NOTES. 
201 
several weeks each amongst the pearl oyster banks in the Gulf of 
Mannar, and have had the experience of the three consecutive 
inspections of March and November, 1902, and March, 1903, and 
also the successful fishery of 1903, from which to draw conclu¬ 
sions. Many hundreds of oysters have been examined, and large 
numbers of pearls have been decalcified. As a result of this work 
they have come to the conclusion that there are several distinct 
causes that lead to the production of pearls in the Ceylon pearl 
oyster ( Margaritifera vulgaris , Schum.). 
(1) Some pearls or pearly excrescences on the interior of the 
shell are due to the irritation caused by Glione , Leucodore , and 
other boring animals. 
(2) Minute grains of sand and other inorganic particles only 
form the nuclei of pearls under exceptional circumstances. 
Probably it is only when the shell is injured, e.g ., by the breaking 
of the 44 ears,” thus enabling sand to get into the interior, that such 
particles supply the irritation that gives rise to pearl formation. 
(3) Many pearls are found in the muscles, especially at the 
levator and pallial insertions, and these are formed around minute 
calcareous concretions, the 44 calcospherules,” which are produced 
in the tissues and form centres of irritation. 
(4) Most of the fine pearls found free in the body of the Ceylon 
oyster contain the remains of Platyhelminthian parasites, so that 
the stimulation which leads to the formation of an 44 Orient ” pearl 
is, as has been suggested by various writers in the past, due to the 
presence of a minute parasitic worm. In all cases, whatever its 
nucleus may be, the pearl, like the nacre, is deposited by an 
epithelial layer. 
These pearls may be conveniently classified as— 
(1) Ampullar pearls, where the nucleus and resulting pearl lie 
in a pouch, or ampulla , of the ectoderm projecting into the mantle. 
The others lie in closed sacs. 
(2) Muscle pearls, formed around calcospherules near the 
insertions of muscles. 
(3) Cyst pearls, formed around encysted parasites. The 
parasite in the case of the majority of the cyst pearls of Ceylon is 
the larva of a Cestode which appears to be new, and will be 
described under the name Tetrarkynchus unionifactor * * The 
younger larval stages have been found free-swimming in the Gulf 
of Mannar and on the gills of the oyster ; later stages are common 
* Cf. The Parasites of the Pearl Oyster, by Arthur E. Shipley, M.A., F.R.S., and 
• James Hornell, F.L.S., in Professor Herdman’s Report on the Pearl Oyster Fisheries 
of the Gulf of Mannar, Part II.. London (Royal SocietvY 1901, see p. 88. 
