148 PROTOZOAN PARASITISM . 



of the length of the body. A skeletal or stiffening 

 structure, the axostyle, extends from the region of 

 the nucleus through the length of the body and pro- 

 jects as a sharp spine from the surface near the 

 posterior end. There is an indistinct slit or cyto- 

 stome at the anterior end near the origin of the flagella 

 opposite to the undulating membrane. 



The nucleus is near the base of the flagella and 

 undulating membrane, is invisible in ordinary active 

 unstained specimens, and its detail is not easily stud- 

 ied even in stained specimens. It is ovoid and has 

 a definite membrane. The distribution of chromatin 

 is not well described, the karyosome is considered 

 to be central. 



The division of the organism is by binary fission, 

 the nucleus undergoing mitosis, according to Kofoid 

 (1915). 



In division the body increases in size, it becom- 

 ing increased laterally more than longitudinally. 

 The nucleus divides and probably the axostyle and the 

 undulating membrane split longitudinally from be- 

 fore backward. The flagella apparently do not split 

 but are evenly divided between the two new organ- 

 isms. The appearance of the dividing organism be- 

 comes shield shaped with an indentation between 

 the two new anterior poles, which may have two 

 flagella each. The undulating membrane may be 

 separated anteriorly and joined posteriorly. An- 

 terior schism proceeds until the organism is com- 

 pletely divided, the posterior extremities adhering 



