296 DR. H. LYSTER JAMESON ON 
a quantity of clustered pearls, mostly of the baroque and seed- 
pearl classes, in the visceral mass. The three examples with 
“pearls in mantle” showed pearls, chiefly in the regions of the 
levator muscles, though some were in the non-muscular parts of 
the visceral body-wall. The specimen with ‘ova of Entozoa in 
liver ” is interesting, as showing the Cestode, Tylocephalum 
ludificans, in its whitish fibrous pearl-like cysts, which on super- 
ficial examination suggest “eggs.” It was in this specimen, 
in 1901, prior to Prof. Herdman’s departure for Ceylon, that I 
first became acquainted with these larve, which Prof. Herdman 
identified as the cause of cyst-pearls. The few observations that, 
[ was able to make at that time led me to the conclusion that 
there was no evidence that this parasite was concerned in pean'- 
formation *, a conclusion that I have, so far, seen no sufficient 
cause for modifying. 
Owing to their age, the state of preservation of these specimens 
was naturally somewhat defective, and for real detailed histological 
work upon the pearl-producing tissues they were quite useless. 
Many of the pearls in these specimens had fallen out of their 
sacs and lay in the bottom of the jar. Some of these, along with 
others picked out of the tissue, numbering 22 in all, were 
decalcified and examined in oil of cloves, and six of them were 
then sectioned and further examined. [Preparations XIV, XV, 
OVE LX hie, aX Kite, TXeXt ys (Bis? Rex Revell Nek val nl, 
figs. 16-18 and Pl. XLIV. figs. 46-48). | 
A large piece of tissue in the wall of the visceral mass, 
measuring about 5x5x4 mm., and containing no less than 
16 pearls, was cut out from the specimen with “ pearls in ovary,” 
decalcified, stained with borax carmine and indigo carmine, and 
sectioned [Preparation XXVIII (Pl. XXX VII. figs. 14, 15)]. 
These pearls were all of the class which I refer to provisionally 
(see below) as muscle-pearls, and were mostly formed around 
central cavities. 
(iii.) Unlabelled Material in the British Museum. 
Mr. Smith also allowed me to examine two unlabelled speci- 
mens of Margaritifera vulgaris in the British Museum, the 
history of which is unknown. One of them was with the example 
in spirit now on show in the Museum, and was accompanied by 
its shell. It is from this example that preparations XX VII and 
XXIX were cut. It contained a large number of muscle-pearls 
and what Prof. Herdman calls “calcospherules” in the left 
mantle-lobe, and in the region of the adductor muscle on the left 
side. The other example had been removed from its shell. 
It contained a large number of clustered pearls, of all sizes, in 
the right mantle-lobe. The tubes in which the specimens were 
preserved contained also a lot of loose pearls which had dropped 
out of both these specimens. 
* In 1902 (25), p. 149, I pointed out that Cestode larve were not surrounded by 
a pearl-sac. 
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