34 CEYLON PEARL OYSTER REPORT. 



scar. Very rarely small ones may be seen along the edge of the adductor. Most 

 frequent of all are pearl masses of irregular or even botryoidal form attached at or 

 adjacent to the levator insertions. Decalcification of these pearls reveals no organic 

 nuclei, whereas the pearls irregularly disposed have cestode embryos as nuclei, exactly 

 as ' fine ' pearls have. 



" Examination of these 30,000 shells gives, therefore, strong confirmatory evidence 

 in support of the. theory set forth by Professor Herdman and myself""" associating 

 such pearls as have no organic nuclei (cestode or other platyhelminthian embryos) 

 with the attachment surfaces of those muscles which are inserted on the shell, 

 especially the small and comparatively weak levator and pallial muscles. Figs. 11 

 and 12 show the distribution in the body of cyst pearls and muscle pearls respec- 

 tively, and fig. 12 is very instructive in showing the perfect way in which the 

 positions of the shell pearls there depicted coincide with the series of pallial muscle 

 scars. 



" Phosphorescent and other Phenomena. 



" On the evenings of April 9th, 10th, 11th, and 12th, when at anchor on the 

 Western Cheval, we beheld a repetition of the strange phosphorescent phenomenon 

 witnessed by Professor Herdman on March 13th, 1902 (see this Report, Part L, 

 1903, p. 81). The display began at about the same hour each evening, varying from 

 8.45 to 9.30 p.m., the sea being dotted with large isolated flashing lights that 

 pulsated and vanished ghost-like at regular and frequent intervals. 



" The rhythmic and progressive blotting out and rekindling of these phosphorescent 

 fires was as if the sea were swept by regularly recurring search -light rays. The 

 beginning of each successive light- wave appeared to lie to the south ; the intervals 

 were approximately of two seconds' duration. All the four nights were dark, but the 

 weather was variable, one night tempestuous, another fairly calm, a moderately strong 

 swell j^revailing the whole time. The displays lasted approximately for an hour each 

 evening. The cause remains undetermined. 



" Trichodesmian calm. During several days in March vast quantities of the red- 

 brown scum of Trichodesmium erythrceum lay profuse and filthy upon the surface of 

 the sea. So abundant was this scum that twice did it extend the period of noontide 

 calm, acting precisely as a film of oil does. At midday when the first puffs of the 

 sea-breeze came out of the north-west, while the breeze was evident enough 

 otherwise, yet it failed for sometime to disturb the surface where lay this scum. 

 Where it was absent, or where the progress of the launch broke a lane through the 

 film, the wind raised ripples and wavelets which little by little spread and encroached 

 upon the Trichodesmian calm. This with the gradual freshening of the wind finally 

 scattered the particles, driving them downwards. 



* ' Brit. Assoc. Report,' Southport, 190-j, p. 695. 



