1S8 



Mr. C. Dobell. 



[Feb. 21, 



and Saprospira, Gross. The four genera may be collected into a single group 

 which I have called the Spirochaetoidea. I have made a careful study of the 

 morphology of two species of Spirochceta (from fresh water) ; four species of 

 Cristispira (from Lamellibranchs) ; nine species of Treponema (eight parasitic 

 forms from various animals and one free-living form from fresh water) ; one 

 species of Saprospira (from fresh water). In addition to these, I have studied 

 in a similar way a large number of flagellate Protozoa, Bacteria, and 

 Cyanophyceae. I have devoted special attention to the forms which are of 

 special importance in the present connection. These are certain spirillar and 

 bacillar forms of bacteria, and the spiral forms {Spirvlina, Arthrospira) of 

 Cyanophycea?. As nearly all these organisms are extremely small, I have 

 naturally paid considerable attention to matters of cytological and microscopic 

 technique. I shall not describe here the methods which I have used, as my 

 aim now is to give my results only. 



The morphological characters which I have been able to establish in the 

 case of the Spirochaets which I have studied are the following : — 



(1) All the Spirochaets possess an elongate and more or less spirally 

 wound body, which is non-cellular.* 



(2) They are flexible — the degree of flexibility displayed differing in 

 different species. 



(3) Antero-posterior polarity is absent in all genera. In other words, 

 during movement either end of the body may function as an anterior or 

 posterior end. 



(4) The body is clothed with a pellicle, the thickness of which differs in 

 the different genera. (In the smallest species of Treponema and Spirochceta, 

 the presence of a pellicle cannot be established with certainty.) 



(5) All the Spirochaets which are sufficiently large for accurate observa- 

 tions to be made in this respect are plasmolysable. (The results of 

 plasmolysis are not identical in all forms. The differences observed appear 

 to be due to corresponding differences in the thickness and nature of the 

 pellicle.) 



(6) No flagella or other special organs of locomotion are present. 



(7) The cytoplasm possesses a peculiar structure — which I have calledf 

 the " chambered structure " — and there is probably a form of chromidial 

 nucleus present. This is true of Cristispira, Saprospira,, and the largest form 



* I cannot agree with Gross, who maintains that the Spirochaets are multicellular. 

 I believe they are all non-cellular ("unicellular "). 



t I have described this in detail in a previous account of Cristispira veneris ('Quart. 

 Journ. Micro. Sci.,' 1911, vol. 56). My description is essentially similar to those 

 previously given (of other species of Cristispira) by Laveran and Mesnil, Swellengrebel, 

 Schellack, and Gross — the differences being in matters of detail. 



