8 Vniversity of California Piiblications in Zoology [Vol. 18 



like the other flagella vibrate in the characteristic wave-like manner, 

 the waves always progressing anteroposteriorly. 



The axostyle lies on the ventral floor extending from the caudal 

 area anteriorly, well into the cytostomal area. It lies in the median 

 plane. Bensen (1908&) describes the axostyle as double, composed of 

 two chromatinic rods ; the blepharoplasts situated at their anterior 

 extremities, each rod continuing posteriorly in a free flagellum. But 

 according to investigations of Kofoid and Christiansen (1915a and h) 

 there is more evidence to show that the axostyle is a single rodlike 

 structure and not a double one, for throughout their study of mitosis 

 in Giardia niuris they found that the axostyle split, forming new ones 

 for the new individuals. In no case did they find four rods, as must 

 be the result of splitting had the axostyle been composed of two rods 

 as Bensen (1908&) believed. My work on Giardia microti confirms on 

 this point the findings of Kofoid and Christiansen. The axostyle may 

 now be said to consist of a single rod, terminating anteriorly with the 

 two blepharoplasts and posteriorly with the two caudal flagella. It 

 is but a single undivided rod except as mitosis approaches. 



In many cases a basal granule can be seen at the point at which 

 the posterior or caudal flagella take origin (pi. 1, figs. 2, 7). It would 

 seem quite justifiable to regard the axostyle as the intracytoplasmic por- 

 tion of the caudal flagella, and therefore probably of flagellar origin 

 (Kofoid and Swezy, 1915). When the axostyle has completely split, 

 one flagellum goes to each daughter axostyle (pi. 1, fig. 9) ; the contin- 

 uity of the intracytoplasmic portions with each caudal flagellum is 

 easily followed. The axostyle was never observed free from the body of 

 the flagellate. It is very flexible and may bend upward and downward 

 or to either side, acting in such a way as to direct the course of the 

 flagellate in locomotion. 



Parabasal Bodies 



The parabasal bodies, composed of one broad, or two narrow bands 

 of deeply-staining material which in some cases appear to be fused in 

 one body, are situated dorsal to the axostyle and at the end of the ante- 

 rior two-thirds of the body (pi. 1, fig. 1). These organs lie in a median 

 plane, extending either to the right or left of the axostyle. In figure 

 8 it seems to lie directly upon the axostyle, or (as in figure 12) it may 

 be connected with the axostyle by one or more slender fibrils. It plays 

 no part in mitotic activity. The character of these bodies in Giardia 

 microti has a striking resemblance to that of similar structures found 

 in G. intestinalis (see Rodenwaldt, 1911). Rodenwaldt (1911) 



