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 Ceylonf that I 

 first became acquainted with these larvae, which Prof. Herdman 

 identified as the cause of cyst-pearls. The few observa,tions that 

 I was able to make at that time led me to the conclusion that 

 there was no evidence that this parasite was concerned in pearl- 

 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 

 tlien sectioned and further examined. [Preparations XIV, XV, 

 XVI, LXXIc, LXXlG, LXXIj (Pis. XXXVII., XXXVIII. 

 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 wdth "pearls in ovary," 

 decalcified, stained with borax carmine and indigo carmine, and 

 sectioned [Preparation XXVIII (PL XXXVII. figs. 14, 15)]. 

 These peai'ls were all of the class which I refer to provisionally 

 (see below) as muscle-pearls, and were mostly formed around 

 central cavities. 



(iii.) Unlahellecl Material in the British Aluseimi. 



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 pi^eparations XXVII 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. 



* la 1902 (25), p. 149, I pointed out that Cestode larva; were not surrounded by 

 a pearl-sac. 



