1917] Boeck: Mitosis in Giardia microti 7 



separation of the axostyle, but as yet there is no mitotic change in the 

 nucleus, or a cleavage of the centrosome. This, however, as will be 

 shown later, is the final step of the preceding mitosis. When the ble- 

 pharoplasts divide, resulting in two smaller blepharoplasts on each 

 axostyle head, there may be also a splitting of the anterolateral flagella 

 extending from the blepharoplasts to the anterior ehiasma, although 

 this condition is variable (pi. 1, figs. 9, 17). 



Of the eight flagella, the anterolaterals, arising from the blepharo- 

 plasts, proceed anteriorly, cross each other to form the anterior 

 ehiasma, and then, going to the sides opposite to their place of origin, 

 lie in the anterior peristome. The intracytoplasmic portions of these 

 flagella fuse or partially coalesce with the anterior peristomal fibrils, 

 and are seen to proceed backward, each one later emerging from a 

 basal granule as a free flagellum. Often the anterolateral flagella 

 fuse or partially coalesce with the anterior peristomal fibrils, thus 

 causing these fibrils to be wider than in their usual state (pi. 1, figs. 

 1,2,7). 



The pair of posterolateral flagella seem to arise, as has been said 

 before, at a point on the axostyle a short distance back from the ble- 

 pharoplasts. This is contrary to the findings of Benson (1908), who 

 pictures each intracytoplasmic portion as having a special point of 

 origin, a basal granule situated alongside of the blepharoplasts. But 

 the evidence on hand in my material does not confirm his findings. As 

 these flagella continue posteriorly in their course, they diverge from 

 the axostyle at an angle of 20° to 30° in a lateral direction. The intra- 

 cytoplasmic portion is more rigid and thicker than that part of the 

 flagellum which continues outward as a free whip. There is no basal 

 granule discernible at the end of the intracytoplasmic portion. 



These intracytoplasmic portions of the posterolateral flagella are 

 close to the surface of the cytoplasm. Observations of living forms 

 show them to be active, as scull-like propellers in the locomotion of the 

 parasite. They vibrate in a co-ordinated wavelike manner from side 

 to side, the vibration starting at the origin of each intracytoplasmic 

 portion and continuing outward to the end of the flagellum. This 

 movement is possibly due to the extreme plasticity of the caudal area 

 of the flagellate 's body. At no time were the intracytoplasmic parts 

 seen to be separated from the body. 



The pair of free ventral flagella take origin at or near the same 

 point at which the posterolateral flagella arise, but they have no intra- 

 cytoplasmic portions. In locomotion they are seen to trail behind, and 



