82 Vniversity of California Publications in Zoology [Vol. 16 



and flagella, the caudal ones being either a new outgrowth or formed 

 by a drawing out of the axostyles at the point of severance, is uncon- 

 vincing in the extreme. Alexeieff (1911) in Hexamitus from Triton 

 cristata gives a more connected series of division figures which are in 

 accord -with those given here. Details of chromatin and nuclear divi- 

 sion he has not figured, however. 



The two types of division shown here differ only in that the spindle 

 formation is intranuclear in Hexamitus ovatus and no membrane is 

 apparent in H. intestinalis, with the lack also of membrane formation 

 in the telophase stage of division in the latter species. The whole 

 process presents man.y points of similarity to that figured for the 

 trichomonad flagellates (Kofoid and Swezy, 1915o, h), notably in the 

 formation of a skein or spireme, a constant number of chromosomes 

 and their division before taking a position on the spindle, and the 

 relation of the flagella to the centrosome or blepharoplast during 

 division. The dissolution of the old nuclear membrane and the for- 

 mation of two entirely new ones may be taken as a step forward, 

 similar to the process evolved in metazoan mitosis. 



The idea has already been brought forward (Kofoid and Swezy, 

 1915a, h) that the axostyle of Trichomonas represents an intracyto- 

 plasmie flagellum, one of the accessory motor organelles of the body. 

 The behavior (during division) of the axostyles in Hexamitus, homol- 

 ogous organs, is strongly corroborative of that interpretation. At 

 this time they may be distinguished from the flagella only by their 

 greater thickness, great motility being shown in the constant change 

 of position to which they are subject. 



Summary 



Cell division in Hexamitus is a simple form of mitosis, initiated 

 by division of the blepharoplasts, followed by longitudinal splitting 

 of both axostyles. Four chromosomes are found on the mitotic spindle, 

 two going to each daughter nuclei. New nuclear membranes are formed 

 inside the old one, which fades out and disappears before the com-' 

 pletion of the process of cell division. 



Multiple fission takes place in the unencysted forms by a series of 

 successive divisions of the two nuclei and the accompanying motor ap- 

 paratus without corresponding division of the cell body, forming a 

 somatella of eight undivided binueleate individuals. These later break 



