SYSTEMATIC DESCRIPTION OF SPECIES. 79 



encysting. Masses of chromatin are formed, connected 

 by thin threads. These divide into fragments, of 

 which the greater number degenerate, but two remain 

 and conjugate (autogamy) , subsequently giving rise to 

 the female gametes. 



The male gamete is distinguished by the appearance 

 of a rounded swelling of the entoplasm in the middle 

 of the body, followed by longitudinal division of the 

 organism, starting simultaneously at both ends. A 

 reduction of chromosomes takes place in the central 

 swelling, thirty-two remaining. Presumably the result- 

 ing individuals conjugate with female forms, but Perrin 

 notes that he was able to observe only a few doubtful 

 examples of cojugation (Fig. 35). 



Fantham confirms Perrin's account of the general 

 form of the nucleus. Further confirmation is needed 

 of the different forms distinguished by Perrin, and of 

 their true meaning, but we may compare Gonder's 

 account of Sp. pinnce. It is noteworthy that Perrin 

 found that not all these spirochaetes had undulating 

 membranes, and also that he observed little difference 

 in the movements of the forms with it and those with- 

 out it. He does not accept the view of Laveran and 

 Mesnil that the organism is furnished with a sheath, 

 rather than with an undulating membrane, but agrees 

 with them that it is a spirochsete, though he describes 

 it as a trypanosome. 



SPIROCH^ETA ANODONT^E. 



(Keysselitz, 1906.) 



This large spirochsete was discovered by Keysselitz 

 in the fresh- water mussel (Anodonta cygnea) ; it also 

 occurs in Anodonta mutabitis. It exists in the crys- 

 talline style, and may also be found in the liver and in 



