518 C. CLIFFORD DOBELL. 



tliroag'liont, and shows no fibrillai' structure in living or 

 properly fixed specimens. It is stained a pink or violet colour 

 by Cliemsa's method, in marked contrast with the general 

 blue colour of the body (see fig. 2, etc.). There is no 

 thickened, chromatic edge to the crista. In fact, it does nob 

 in any way resemble tlie undulating membrane of a trypano- 

 some. 



In macei'ated individuals the crista may present a very 

 different appearance (fig. 3). It becomes greatly enlarged 

 and distorted, and shows a very definite fibrillar structure. 

 This is an artifact, and though it may indicate that the crista 

 is really composed of fibrils arranged longitudinally, it 

 must not be forgotten that ia normal individuals it appears 

 absolutely homogeneous. This fibrillar appearance has often 

 been described as the normal structure of the " undulating- 

 membrane" of Cristispira — which it certainly is not. 



The crista of 0. veneris is therefore a delicate, uniform, 

 band-like appendage, wound spirally round the body, and 

 extending almost to the ends. It is always present, and has 

 no resemblance to the undulating membrane of a trypano- 

 some. It serves, apparently, as a rigid lateral fin-like exten- 

 sion of the body, in the performance of the screw-like 

 movements of the organism. Some further account of some 

 of the previous interpretations of this structure will be found 

 on p. 528. 



Structure of the Protoplasm. — As I have already 

 noted, the protoplasm of the living organisms appeai-s homo- 

 geneous. In stained specimens, however, it has a distinct and 

 highly characteristic structure. This structure has been 

 observed by Schellack and Gross, though the interpretations 

 of these two observers differ. 



If a Cristispira be fixed by exposure to osmic vapour for 

 about thirty seconds, then transferred immediately (without 

 any drying being allowed to take place) to absolute alcohol 

 for ten minutes, then stained by Giemsa^s method, and 

 examined in the manner already described (p. 509), it is seen 

 to possess a structure like that of the individual shown in fig. 



