ON CRISTISPJEA VENERIS NOV. SPEC. 509 



visiting Ceylon in 1909, during- my tenure of the Balfour 

 Studentship of Cambridge University (cf. Dobell, 1910). 

 As the organism is of large size, I took the opportunity of 

 investigating its structure and life-history as far as possible. 



All the specimens of Venus casta which I exannned were 

 taken from Tamblegam Lake/ in the Eastern Province of 

 Ceylon. These molluscs — together with others — were collected 

 for me by Di"- Willey, at Xiroddumunai, and sent thence to 

 me in Trincomalee — about eight miles distant. With Dr. 

 Willey's assistance I also examined some of the molluscs at 

 Niroddumunai soon after they had been captured. I take 

 this opportunity of again thanking Dr. Willey for his kind 

 collaboration. 



A crystalline style was present in 50 per cent, of the 

 specimens of Venus casta which I examined. In every 

 instance in which a style was present it was found to be 

 infected with Cristispiraj. Examination of the contents 

 of the CBSophagus and stomach of individuals possessing no 

 crystalline style was in every case negative ; but only a few 

 of these individuals were carefully examined. TheCristi- 

 spirte were usually present in large numbers, and were always 

 very actively motile when first removed from their host. 



After studying the living organisms, I made a number of 

 permanent preparations in order to investigate finer details 

 of structure. The method employed was the same as that 

 which I have frequently used with success in studj'ing similar 

 forms. Bacteria and blood-inhabiting Protozoa, I made moist 

 films of the substance of the crystalline style, fixed them by 

 exposure to osmic vapour followed by absolute alcohol, and 

 then stained them by Giemsa's or Leishman's modification of 

 Romanowski's stain. The films were then washed in water 

 and allowed to dry, or previously differentiated in weak 

 alcohol. They were examined under an immersion in cedar- 

 wood oil. This method gives, I believe, very accurate results 

 when properly employed. The fixation with osmic vapour 



1 Tamblegam Lake is a salt-water lake, connected with Koddijar 

 Bay. All my observations were made in September, 1909. 



