268 DR. Hl. LYSTER JAMESON ON 
Mr. Southwell (40, p. 194), referring to the caleospherules 
causing “ muscle-pearls,” says : 
“The origin of the latter bodies is quite unknown, 
although it seems almost certain that they are depositions 
from the blood.” 
Again, in a later paper (42, p. 128), Mr. Southwell says : 
“ Other pearls are also found in the Oyster, but they have 
no organic nucleus. Such pearls are termed muscle or seed 
pearls. ‘Their origin is obscure, but they are always found 
near the muscle insertions, and are believed to be formed 
round a calcospherule of excretory origin, or by the sheer of 
muscles moving in different planes.” 
In the first mentioned of the above papers (40), he goes on to 
say: 
“Considerably more pearls are formed round calcospherules 
than round parasites, the ratio being about 13 to 1. They 
are therefore of considerable commercial importance.” 
Unfortunately, Mr. Southwell does not give the number or 
sources of the pearls on which this statement is based, although 
if is quite clear, from the observations of Prof. Herdman and 
Mr. Hornell, that ‘‘ muscle-pearls ” are characteristic of certain 
localities, and “ cyst-pearls ” of others, and that the ratio may vary 
greatly on different banks. 
My own observations on ‘* Muscle-pearls” and on the nature of 
the so-called “ caleospherules” are given in a later part of this 
paper. 
(vi.) Cestode Larve. 
Of fine or “ Orient” pearls Prof. Herdman and Mr. Hornell 
claimed that the most frequent nucleus is a Cestode larva. In 
their ‘ Conclusions on Pearl-Formation ” (Report V. p. 29) they 
maintain that their investigations have shown * that in J/argariti- 
fera vulgaris, at Ceylon, the production of the *‘ Orient’ pearl is 
dependent upon Cestode infection and that the species mainly 
concerned is Tetrarhynchus unionifactor,” and in the General 
Summary of their Ceylon Report (V. p. 127) they say : 
“The majority of these fine pearls contain as their nuclei 
the more or less easily recognisable remains of certain 
Platyhelminthian parasites, which we identify as the larval 
condition of Cestodes belonging to the genus Vetrarhynchus.” 
It is stated several times that this supposed identification was 
made during Professor Herdman’s second cruise in March 1902, 
but its elaboration must have been, in great part, the work ot 
Mr. Hornell at a later date. The narrative of the Cruise 
(Report I. p. 70), published in 19038, states, in a paragraph 
apparently inserted between the records of March 6th and 7th: 
“In the intervals of dredging and when moving from 
place to place, we were now continuously engaged in 
[10] 
