540 C. CLIFFORD D()BFr,L. 



Viiillemin, P. (1905). — " Sur la denomination de I'agent presume de la 



syphilis," ' C R. Acad. Sci./ vol. cxl, p. 1567. 

 Ziilzer, M. (1910). — '" Ueber Spirocliaita plicatilis nnd Spirulina," 



' Zool. Anz.,' Bd. xxxv, p. 795. 



■ EXPLANATION OF ]^LATE 20, 



Illastratiiig Mr. C. Clifford Dobell's paper " Oq Oristispira 

 vetieri.s nov. spec.^ and the Affinities and. Classification 

 of Spirocliaits." 



[All figures are drawn from stained preparations of Oristispira 

 veneris n. sp.,from the crystalline style of Yenus (Meretrix) casta 

 Chem., taken in Taniblegam Lake, E. Province. Ceylon. The drawings 

 were made under a Zeiss 2 mm. apochromatic oil-immersion, with com- 

 pensating oculars 6, 12, and 18. The magnification of the figures is 

 approximately 2U0O diameters.] 



Fig. 1. — An average-sized individual, in optical section. The general 

 form of the body is well seen. Note also the chambered structure of 

 the cytoplasm and the arrangement of the purple-stained granules. 

 (Osmic vapour 30 sees, absolute alcohol; Giemsa's stain.) 



Fig. 2. — A somewhat extended individual, showing the disposition of 

 the crista and the structure of the protoplasm. The body is seen in 

 optical section, but the crista is shown as it appears when focussed 

 carefully at different levels. (Osmic vapour [several minutes] : absolute 

 alcohol, Giemsa.) 



Fig. 3. — An individual which has been macerated in a drop of sea- 

 water, allowed to dry, then fixed in absolute alcohol and stained Ity 

 Giemsa's method. The organism has undergone plasmoptysis, and 

 the crista shows a fibrillar structure. 



Fig. 4. — A dividing oi'ganism in the stage of incurvation. (Osmic 

 vapour, absolute alcohol, Giemsa.) 



Fig. 5. — Part of an almost completely divided organism in incurvation 

 stage. The upi^er end corresponds with the upper end of fig. 4, being 

 the point at which fission occurs. (Slightly more highly magnified 

 than the other figui*es.) (Osmic vapour, absolute alcohol, Giemsa.) 



Fig. 6. — An individual which is almost completely divided into two. 

 Stage following incurvation. At a, a darkly stained chamljer. (Osmic 

 va^wur [several minutes'^, absolute ;^l(•oIl()^ Giemsa.) 



