No. 593] THE PROTOZOAN LIFE CYCLE 269 



tion. A visible expression of such differentiation is seen 

 again in the chromidia formation of Sarcodina and in the 

 dimorphic gametocytes of foraminifera and Sporozoa. 

 The reorganization phenomena are quite as complicated 

 and as far reaching as after encystment, and the end result 

 is the same, a de-differentiated protoplasm and a new indi- 

 vidual with a high potential of vitality. If fertilization is 

 prevented the differentiated macro- and microgametes die 

 as do metazoan eggs and spermatozoa, and a similar result 

 follows the continued culture of free-living ciliates in 

 which conjugation, or its equivalent, asexual endomixis, is 

 prevented. 



In all life histories we find more or less regular cycles 

 of vegetative and sexual phases, complicated by more or 

 less active asexual and sexual reproduction. In parasitic 

 forms it is possible, I may say probable, that reorganiza- 

 tion and renewal of vitality take place during encysted 

 stages as Schaudinn, Wenyon and others have held for the 

 genus Entameba; or, as in Paramecium, they may take 

 place without encystment in types like Plasmodium as de- 

 scribed by Schaudinn. The processes of autogamy, so- 

 called, described for different types of Entameba, may be 

 interpreted as asexual endomixis, and the conflicting 

 views as to the significance of nuclear structures in Enta- 

 meba coli, E. histolytica, E. tetragena and E. minuta, may 

 all be reconciled when this possibility of asexual reorgan- 

 ization is applied to the various parasitic rhizopods. 



With Plasmodium, the principle of asexual reorganiza- 

 tion and renewal of vitality, or parthenogenesis, has long 

 been called upon to explain malaria relapse. The process, 

 as described by Schaudinn, is too familiar to need repeti- 

 tion here. Despite the objections which have been raised 

 in recent years against this interpretation, it must be ad- 

 mitted that no a priori difficulty stands in its way. It 

 is evident from experiments that the protoplasm of an old 

 race is more stabile than that of a young race, possibly due 

 to accumulation of products of metabolism in the former, 

 either for a useful purpose, as in the storage of yolk ma- 

 terial in a female cell, or for some harmful purpose, as in 



