POLYTOMELLA CITRI, SP. NOV. 225 



importance of which must be realized when we consider its 

 position on the threshold of the Phytomonadina. 



LIFE HISTORY. 



With the exception of Polytomella agilis and Dunaliella salina 

 the descriptions of the members of this family would lead us to 

 believe that the life history consists of two phases, binary fission 

 during the active stage and rest and reorganization through 

 encystment. Dangeard (1889) describes the cysts of Polyble- 

 pharides as spherical bodies with a gelatinous wall. This is the 

 only one which has such a covering. To the same author is due 

 the observation that Pyramimonas forms cysts with a very tough 

 membrane. Germination of the latter was not observed, but in 

 the former it gave rise to a single organism, which, after exhibiting 

 typical amoeboid movement for several minutes would assume the 

 usual shape and swim off by the activity of their flagella. This 

 same observation was made on Polytomella citri. Hamburger 

 (1905) noted the formation of cysts by Dunaliella and also saw 

 numerous empty shells but did not observe any in the process of 

 excystment. The cysts of Stephanoptera are spherical and have a 

 very heavy wall. Dangeard mentions the fact that a few of these 

 had two nuclei, and suggests that there may be some autogamous 

 process during encysted life. The binucleate condition, however, 

 probably does not have any more significance here than it does in 

 the active stage of Polytomella citri, where we have interpreted it 

 as representing cases of cytodierisis being prevented from 

 following nuclear division. 



Conjugation has been figured by Aragao for Polytomella agilis 

 and by Teodoresco for Dunaliella. In both cases the figures and 

 description are very incomplete and unconvincing. There are 

 none of the few figures given that could not more easily be 

 interpreted as stages in fission than as representing conjugation. 

 This is especially true for the work of Aragao. In spite of the 

 fact that sexual reproduction probably plays no part in the life of 

 most of the members of this family, we would not be surprised to 

 find sexual processes in Dunaliella because of its near relationship 

 to Chlamydomonas . However, until a more adequate study has 

 been made with this problem in view it is well to be hesitant in 



