42 University of California Publications in Zoology [Vol. 20 



INTRODUCTION 



Among the instances of parasitism by the Protozoa in the alimen- 

 tary tracts of the Metazoa, none exceeds that found in the termites 

 as to the relative volume of the invading parasites, the diversity of 

 organization found among them, and the degree of specialization 

 which they attain. In the vanguard of this evolutionary development 

 stands the genus Trichonympha discovered by that pioneer American 

 investigator, Dr. Joseph Leidy, who in 1877 and 1881 first revealed 

 this teeming menagerie of termite parasites to scientific view. 



The extent of specialization attained by Trichonympha and its 

 allies has obscured their relationships, allied them at first with the 

 ciliates, and obliterated their true affinities with the flagellates. The 

 purpose of the present paper is in part to place the flagellate origin 

 and relationships of the Trichonj-mphidae on a firm cytological foun- 

 dation. It is also our aim to set forth the most complicated neuro- 

 motor system thus far known among the Protozoa, to analyse its 

 elements, relate them to the elaborate motor activities of the indi- 

 vidual, and trace their behavior during the mitosis of this highly 

 specialized cell. 



The degree of structural complexity, the extent of the coordinated 

 mechanism, the number of its constituent elements, and the striking 

 similarity of their interrelations in Trichonympha to those obtaining 

 in multicellular organisms, is illuminating as to the biological sig- 

 nificance of cellular organization. This organism is a single cell, with 

 one nucleus, yet it has attained a degree of structural complexity and 

 functional diversity in respect to one organ .system comparable almost 

 with that of its host and surpassing that of many of the lower Meta- 

 zoa. The multicellular state is plainly not an essential condition for 

 evolutionary specialization and functional efficiency, except as it places 

 limits on the size of organisnus and on developmental processes arising 

 therefrom. The differentiation of organs within the confines of a 

 single cell is here accomplished with a perfection comparable with that 

 where the organ is a complex of diverse cells instead of one of many 

 parts within a single cell. The organism and not its cells is the 

 fundamental basis of differentiation. 



