STUDIES IN THE LIFE-HISTORY OF EUGLENA. 345 



Such a type of organization and behavior of related and kinetic 

 elements is what one might expect in so primitive an organism as 

 Euglena. We have many valid reasons for believing that within 

 this group are to be found the progenitors of the other groups of 

 Protozoa. As evolution progressed toward the rhizopod type, 

 exflagellation might easily be conceived as a process of inhibition 

 of the development of the kinetic complex from the endosome of 

 the nucleus. When conditions in the cycle of an amoeba, e.g., 

 Nagleria gruberi, are appropriate, flagellation is stimulated and 

 we see the complex arising from the endosome as in Euglena. 



In those flagellates which have a more diverse series of life 

 habits and hence greater complexity of structure, such as 

 Trypanosomes, Devescovina, Crithidia, Lophomonas , Calonympha, 

 etc., we find a type of organization easily derived from some stage 

 shown in the development of Euglena. In these parasitic 

 flagellates which show the presence of a permanent parabasal body 

 in connection with the motor apparatus, we can easily conceive 

 that the chromatoid residue which remains in connection with the 

 motor apparatus in Euglena agilis, only during the late division 

 stages and the reorganization period, becomes a permanent 

 organelle of the cell. Such a change might be brought about 

 through the greater demands made upon the motor apparatus 

 when the organisms become adapted to a dense medium. In E. 

 agilis the residue serves as a temporary reserve only, for the 

 kinetic elements of the cell and becomes disconnected ffom them 

 as soon as the new flagellum begins to function actively. A 

 permanent reservoir of substances to be used by the organisms 

 in its kinetic activities is required by the parasitic flagellates. 

 This need is met by the parabasal body. 



We may draw the following conclusions from the preceding 

 discussion : 



(1) The endosome in Euglena agilis is the ultimate source of all 

 the kinetic elements of the cell, but does not contribute to the 

 formation of the chromosomes. 



(2) An endobasal body is located in the endosome and gives 

 rise by division to a chromatoid mass, the kinetic complex. This 

 migrates to the periphery of the nucleus where it divides, the 

 daughter halves passing to the approximate poles of the division 



