164 D - H - WENRICH. 



The flagellar situation calls for special comment. It is difficult 

 to understand why, by actual count, approximately 40 per cent, of 

 the pcllucida should have four, 40 per cent, have six, and the re- 

 maining 20 per cent, either two, three, or five flagella. Six flagella 

 can be accounted for by assuming an abnormal doubling coordi- 

 nated with the hypertrophy and amitosis of the nucleus. Three 

 flagella would occur as a result of the division of a six-flagellated 

 individual or as a result of recent transformation from the type. 

 As shown in Fig. 20, transformation may be accompanied by the 

 addition of one flagellum, possibly on account of the hypertrophy 

 of the nucleus, thus giving four. Two-flagellated individuals 

 would result from the division of those with four. The occurrence 

 of five-flagellated individuals is a further indication of instability 

 of flagellar conditions and may indicate the addition of two instead 

 of one or of three flagella. 



The rareness of transition stages compared with the number of 

 pcllucida can be explained as follows : Division of the green variety 

 appears to be rare within the host and when it does occur seems to 

 result in pellucid individuals (Figs. 22 to 26). Pcllucida, once 

 established, however, seems to multiply relatively rapidly by both 

 mitotic and amitotic divisions, thus enabling it to outnumber the 

 type. The infrequency of transformations would harmonize with 

 the fact that pcllucida has not been found in any of the tadpoles 

 of Rana palustris nor in the tadpoles of other species examined in 

 1923 up to August 15. In tadpoles examined late in 1922 up to 

 January, 1923, the green variety was still found, but not the color- 

 less one. This fact also points to the green variety as the stable, 

 persistent one, while pcllucida appears to be neither stable nor 

 persistent. 



One is tempted to regard the entire situation here dealt with as 

 revealing an uncompleted series of stages in the evolution of a 

 colorless parasite from a free-living, green euglenoid flagellate. It 

 might be assumed that, since Euglenamorpha (type) is still green-, 

 it can not have become completely dependent on the tadpoles ; that 

 adaptation between the invader and its host is not yet perfected ; 

 that in its as yet not thoroughly accustomed surroundings within 

 a host it occasionally undergoes the changes recorded above and 

 becomes the variety pellucida; that this variety has not completed 



