354 KOFOID AND SWEZY. 



direction of permanently multinucleated multiflagellated Trichonym- 

 phida. 



The occurrence in this important order of Euflagellata of a definite 

 multinucleate stage composed of merozoites forming a common Plas- 

 modium which for a brief time at least lives an individual life of its 

 own,. is, we believe, of very great general significance and one, more- 

 over, very largely if not wholly unrecognized. This has resulted from 

 the dominance in developmental textbooks of the Gastraea Theory 

 and the prevalent but mistalcen use of Pandorina and Volrox as transi- 

 tion types between Protozoa and Metazoa. We will not develop 

 this matter farther here, but in passing desire to emphase this multi- 

 nucleate Plasmodium as an initial stage in the formation of aggregates 

 which ultimately become the Metazoa. This stage is, however, only a 

 multinucleate, not a multicellular individual. The formation of such 

 indiAiduals at certain periods in the life-history of the lower Protozoa, 

 the Mastigophora and the Sarcodina, as well as in the more highly 

 specialized Sporozoa and Ciliata, is, in our opinion a phenomenon of 

 fundamental evolutionary significance. We have therefore used for 

 it the prophetic name of somatella. 



The nature of the organism which forms the plasmodium or soma- 

 tella is naturall}^ a matter of great interest morphologically, phylo- 

 genetically, and physiologically. We have been unable to obtain 

 conclusive evidence as to its relationship to other stages or its inducing 

 causes. Binary fission occurs in trichomonads in cycles or waves, 

 at least this stage is found abundantly only in occasional individual 

 hosts. In like manner multiple mitosis is restricted in its occurrence. 

 It appears to occur at certain phases of the life-history, or under cer- 

 tain conditions of the environment, or both. We have not found 

 gametogenesis, nor gametes, nor any evidence that the organism giv- 

 ing rise to the plasmodium is a zygote. Should this ultimately prove 

 to be the case the name somatella for the plasmodium phase will then 

 be doubly applicable. 



Addendum. 



Since the completion of this manuscript we have received the 

 paper of Janicki " Untersuchungen an parasitischen Flagellaten II." 

 (1915) in which he adds much to our knowledge of the Trichonym- 

 phida and trichomonads. Unfortunately his material has not per- 

 mitted a full analysis of all stages in mitosis or of the origin and fate 



