TRICHOMONAD FLAGELLATES. 331 



an advantageous position of the undulating membranes and the two 

 merozoites pull apart. 



These stages might superficially simulate certain aspects of con- 

 jugation of gametes, especially such a position as that at 2:12. How- 

 ever, no instance of end to end conjunction with the cytostomes and 

 flagella apposed were noted in this weird dance of monads. The 

 necessity of caution in the search for indications of sexual reproduc- 

 tion in preparations is apparent in the light of this aspect of behavior 

 of the living merozoites in the late stages of mitosis. 



The Plane of Division. 



The question as to the direction of the plane of division in binary 

 fission has been raised by Martin and Robertson (1911), who find in 

 Trichomonas (= Tetratrichomonas) gallinarum that the division may 

 occur in any one of three planes, longitudinal, transverse, and oblique, 

 the initial direction depending largely upon the direction outgrowth 

 of the new chromatic line. 



In any attempt to apply to the phases of mitosis the morphological 

 axes of the free-swimming vegetative phase it is obvious that due 

 regard must be given to the fairly constant relations of the organelles 

 of that stage to its fundamental axes. The blepharoplast lies anterior 

 to the nucleus, and the undulating membrane, marginal filament, 

 chromatic basal rod, and axostyle are, in the main, longitudinal in 

 position. In the mitotic phases on the other hand, the body is dis- 

 tinctly amoeboid and its metabolic changes induce a shifting of these 

 organelles and of their derivatives and new formations so that these 

 original relations to the axes are variously disarranged (Fig. F). 

 These configurations are constantly changing as will be seen in our 

 figures of these stages. It is therefore unsafe to conclude that the 

 relations of organelles in a given preparation of a telophase are indica- 

 tive of the plane of division, or even of the final act of plasmotomy, 

 for it is probable from our observations on living material that final 

 separation is wont to take place when the daughter blepharoplasts 

 are 180° apart (PI. 4, Fig. 39). According to these writers this would 

 be a transverse division, but it is really only a transverse plasmotomy, 

 the final act in fission, and not the one which reveals the true morpho- 

 logical relations of the plane of division. 



The interpretation of the plane of division should be based on the 

 division of the organelles which bear relations to the axes. In the 



