268 DR. H. LYSTER JAMESON ON 



Ml'. Southwell (40, p. 194), referring to the calcospherules 

 causing " muscle-pearls," says : 



" The origin of the latter bodies is quite unknown, 

 although it seems almost certain that they ai-e 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 ax-e termed muscle or seed 

 pearls. Their origin is obscui-e, 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 pf 

 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 pai^asites, 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 

 it 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 diff'ei'ent banks. 



My own observations on " Muscle-pearls " and on the nature of 

 the so-called "calcospherules" are given in a later part of this 

 paper. 



(vi.) Cestode Larvce. 



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 Margariti- 

 f'e.ra 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 Tetrarhynchus.'' 



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 gi-eat part, the woi-k of 

 Mr. Hornell at a later date. The nairative of the Cruise 

 (Report I. p. 70), published in 1903, states, in a paragraph 

 apparently inserted between the records of Mai'ch 6th and 7th : 



'• In the intervals of dredging and when moving from 

 place to place, we were now continuously engaged in 



