ON CPJSTISPIRA YENEKIS XOY. SPEC. 517 



Neither in living nor in fixed and stained specimens can 

 any structures comparable with flagella be seen. 



Like other Cristispirte, C. veneris has a flexible body. 

 It may be noted, however, that in living and actively moving 

 individuals the body is kept relatively rigid — flexibility being- 

 chiefly observed in slowly moving (? abnormal) individuals, 

 and indicated by the irregular spiral conformation often 

 observable in fixed and stained organisms. I believe that 

 bending movements occur ver}' seldom in normal active indi- 

 viduals. The ordinai-y movements of C. veneris are similar 

 to those of C. balbianii, which have already been described 

 by Perrin (1906). 



The two most important characteristics of the Cristispirte 

 are the crista and the structure of the protoplasm. I will 

 now describe these in detail in C. veneris. 



The Crista. — This structure, formerly called the " undu- 

 lating membrane " on account of its supposed homology with 

 the undulating membrane of trypanosomes, has hitherto been 

 correctly interpreted — I believe — by Gross alone. The name 

 crista, or crest, which he has proposed for it, appears to me a 

 convenient and suitable one. I shall therefore adopt it. 



A crista is present in every individual which I have 

 examined in the living condition or in properly fixed and 

 stained prepai-ations. In dried Giemsa preparations, it may 

 be torn and distorted and sometimes appear completely 

 lacking, but this is due to the drying which has taken place 

 before fixation, and is therefore not a normal condition. In 

 all cases in Avhich proper fixation with osmic vapour has been 

 effected, the crista is present and presents the same charac- 

 teristic appearance. 



The crista is in the form of a narrow band, radially situate 

 on the surface of the organism, and spirally disposed (see fig. 

 2). It does not as a rule reach the extreme ends of the 

 organism, and appears to me to be a simple prolongation of 

 the membrane which clothes the body. At the ends it merges 

 gradually into this, and no structures comparable with basal 

 granules or blepharoplasts are present. It is homogeneous 



