HORNELL— ANATOMY OF PLACUNA 51 



point. The contents are then placed in a tub and allowed to remain for three days 

 till thoroughly putrified. 



When thus prepared the rotten mass is taken up, a small quantity at a time, and 

 rubbed well between the palms of the hands, and allowed to drop into a dish of clean 

 water, where the small pearls fall to the bottom. From time to time the dirty water 

 is decanted an 1 replaced by clean. So the process proceeds till all the flesh has been 

 treated, when, after final rinsing, the seed pearls, called selisip by the Bajaus, are 

 strained off, cleaned and dried, and made ready for the market. 



They are sold by weight ; the prices paid generally give the Bajau divers a fair 

 return for their labour. 



The Borneo seed pearls are bought up by Chinese dealers and exported to China, 

 where the bulk is used in the preparation of various quaint medicines. The Chinese 

 specially esteem pearl medicaments in diseases of the eye, and I have been told by a 

 Chinese doctor that ground-up pearls are considered a specific for syphilis. 



Some of the produce of the Ceylon Placuna fishery also finds its way to China, 

 but the bulk from Ceylon and Sind is consumed in India, either as a component in 

 native medicines, or calcined to form a luxurious form of chunam to smear on betel 

 leaf used in chewing, or as a cosmetic by native ladies. The value of the Sind 

 produce is given as Es. 15 per tola, the same rate as that current in Ceylon, where 

 one rupee's weight (equivalent to one tola) of these pearls passes current at a similar 

 price. Any exceptionally fine and large pearls are, however, taken out from the bulk 

 and sold separately. 



Before entering upon the detailed description of the anatomy and histology of 

 this mollusc, it affords me great pleasure to acknowledge my indebtedness to two 

 helpers, Mr. T. Southwell, A.R.C.S., and Mr. George Henry, whose skilled assistance 

 was always most willingly given. Mr. Southwell was kind enough to prepare and cut a 

 large series of serial sections of young individuals, and to help very considerably in 

 working up this material, while the extent of Mr. Henry's help may be gauged by 

 reference to the very beautiful drawings which add so much to the value of this paper. 



To Mr. Edwin Wilson, Cambridge, I also tender my sincere thanks for the great 

 care and skill he has bestowed in reproducing the drawings upon stone ; the result is 

 everything I desired. 



THE SHELL. 



The shell of Placuna placenta in the fully-grown condition is free, greatly com- 

 pressed, and distinctly, though slightly, inequivalve. The outline is sub- orbicular, 

 the longitudinal axis (length) to the vertical axis (height) being an average of 

 155|^mm. to 142|-mm. for a number of the oldest generation of these shells collected 

 in Lake Tampalakam in 1905. Strangely enough, 155 mm. by 142 mm. were the 

 precise measurements of the largest living specimen I have collected in the. Gulf of 



