1922] Kofoid-Swezy : Mitosis and Fission in Giardia enlerica 207 



The anterolateral flagcllum (ant. lat. fl., fig. B) passes anteriorly 

 in a laterally convex arc to the anterior node (ant. node), which in an 

 earlier paper (Kofoid and Christiansen, 1915) was called the anterior 

 chiasma, a laterally extended granule. From this point, it is impos- 

 sible in the free stage to determine whether on leaving the node the 

 flagellum crosses over to the oppcsite side, or bends abruptly laterally 

 on its own side. Either course is possible. The latter alternative seems 

 more probable in case Giardia has been derived from Chilomastix by 

 the morphological reversal of one daughter at mitosis (see Kofoid and 

 Swezy, 1920). The origin of the node, however, in the prophase (figs. 

 F to K) with the outgrowth of new anterolaterals indicates unmis- 

 takably a contact rather than a cross-over of the flagella. We therefore 

 substitute ' ' node ' ' for ' ' chiasma ' ' to avoid the connotation of a ero.ssiug 

 and to establish in its place one of connection only. 



From this node, the flagellum runs laterally dorsal to and within 

 the anterior peristomal fiber to near the middle of the lateral pei-istomal 

 arc where it crosses that fiber, uniting with it in a slight angular 

 prominence in its course, and emerges posterolaterally as a free flagel- 

 lum. Its intracytoplasmic part stains more lightly than the adjacent, 

 peripheral, peristomal fiber, except .just before mitosis, when it is 

 noticeably thickened and larger than the peristomal fiber. There is 

 no distinct basal granule at or near its point of emergence from the 

 cytoplasm in G. ent erica. It is distinct from the peristomal fiber on 

 careful focusing, though often confused with it by earlier investigators. 

 The level of emergence of this flagellum appears to be characteristic 

 in G. enterica, as compared with G. mitris and G. microti, in that it is 

 somewhat more anterior. In twenty-five individuals chosen at random, 

 it was distinctly anterior to the middle in eighteen (pi. 23, fig. 1), 

 median in five, and slightly posterior in two only. Obviously, in a 

 mobile organ such as the sucker, the state of contraction of the peri- 

 stome and the localization of the contraction modify the relative 

 positions of the emergence of this flagellum. 



The posterolateral flagella {post. lat. fl., fig. B) emerge postero- 

 laterally at the level of the constriction of the tail. Their points of 

 emergence are about the same distance from those of the anterolaterals 

 as the latter are from the apex of the body. Their intracytoplasmic 

 parts [intracyt. post. lat. fl.) pursue an anteromesad course, appar- 

 ently uniting with the posterior peristomal fibers as the.y curve 

 anteriorly and merge with the axostyles on their way to the blepharo- 

 plasts. Presumably they join the blepharoplasts of their respective 



