THE CEYLON PEAHL-OYSTEli. 267 



a nucleus is absent to two alternative causes. In tlie first ca^e, tlie 

 Ti'i'niatode described in my paper on the Origin of Pearls in 

 the P. Z. 8. for 1902 (25) may migrate out of tlie sac, in which a 

 peai-1 without any nucleus, or with a nucleus consisting of a few 

 lesidual giunules, may subsequently be formed. In the second 

 case, in certain localities, MtjIUus edulis produces pearls through 

 an agency (which I am at present tiying to investigate) other than 

 Vermian. These pearls may have as nuclei either a few dark 

 granules or nothing that can be detected without the use of much 

 higher magnification than 100 diametei'S. One of them is shown 

 at C in text-figure 33 (p. 277). 



(v.) M^tscle- Pearls. 



The discoveiy of "muscle-pearls" was, I believe, first announced 

 at the British Association Meeting in September 1903. 



Under this name (Bi-it. Assoc. Report, Southport, 1903, p. 695) 

 Prof. Herdman distinguishes pearls formed " around minute 

 calcareous concretions, the ' calcospherules,' which are produced 

 in the tissues and form centres of irritation." They occur " most 

 abundantly in the muscular tissue near the insertions of the 

 levator and pallia! muscles." (Report, Part V. p. 27.) Herdman 

 and Hornell say, speaking of muscle-pearls : 



" it seems probable that these have been formed by the 

 deposition of calcareous matter around a minute calculus in 

 the tissues " . . . . " The Muscle pearls when present are 

 usually abundant, and when examining under the microscope 

 a young peail of this kind, in siiti, it is common to find a 

 large number of minute calcareous depositions or calco- 

 spherules scattered in the neighbouring tissue. It is probable 

 that the muscle pearls are formed around these microscopic 

 calcos[)herules as centres of irritation, and as these [? theii'] 

 positions are invariably in our experience close to the surface 

 of the muscle or the mantle, there is no difiiculty in under- 

 standing that there, if anywhere, ectoderm cells might 

 migrate to the soui'ce of iii-itation and thus be responsible 

 for the deposition of a pearl." (Report V. p. 27.) 



Muscle-peai'ls are especially numerous in certain localities ; 

 Prof. Herdman instances (Report V. pp. 30-31) that they were 

 particularly numerous on the S.E. Oheval Paar in 1902 and 1903, 

 and 



" that the vigorous and healthy oysters of the Eastern Cheval 

 and Periya Paar Karai produce piactically all the examples of 

 this class of pearls," 



the numbers produced on other banks being insignificant. 



Mr. Hornell, speaking of an examination of a number of pearls 

 attached to the shell, states that " decalcification of the pearls 

 attached to muscle-scai's i-eveals no organic nuclei, whei'eas the 

 [attached] pearls irregularly disposed have Cestode embryos as 

 nuclei, exactly as ' fine ' pearls have." (19, p. 12.) 



