1922] Kofoid-Swezy: Mitosis and Fission in Giardia enterica 209 



flagellum at its tip and in being more condensed and more deeply 

 stainable, though not in contractility and its general morphological 

 relations. 



It is to be expected, in so diverse a group as the polymastigote 

 flagellates, that there will be a wide range of form, development, and 

 possibly of modifications of function, in so fundamental an organ as 

 the axostyle, that these diversities will increase as our knowledge of 

 the group is extended, and that the evidence for the homology of the 

 diverse types will be strengthened as more types come to light. 



The parabasal bodies (par. h., fig. A) are a pair of comma-shaped 

 structures lying in the cytoplasm on the dorsal side, just posterior to 

 the middle of the body and to the posterior peristomal fiber. 



Their position in the cytoplasm is in sharp contrast to that of all 

 otlier intracytoplasmic structures which trend more or less posteriorly. 

 The parabasals, on the other hand, generally lie transversely or 

 obliquely to the major axis with their larger blunter ends near the 

 axostyles and the tapering pointed ends directed laterally, indifferently 

 to right or left or obliquely dorsally, and reaching, in ventral or lateral 

 view respectively, about half the distance to the periphery. Their 

 length in the free stage is equal to or a trifle more than that of the 

 longer axis of the nucleus. They are curved bodies, shaped like a 

 comma without a head, and taper from a bluntly rounded, larger end 

 directed mesially, to a finely pointed end directed peripherally. From 

 their bhuiter ends a fine thread, the parabasal rhizoplast (pi. 24. 

 fig. 9; par. b. rhiz.. fig. A), runs anteriorly into the region of the 

 axo.style, and presumably thence to the blepharoplast. Rodenwaldt 

 (1912) incorrectly denies that these bodies have any relation to the 

 fibrillar system. The individuals so oriented a.s to exhibit the parabasal 

 rhizoplast are rare, and long searching of abundant material has been 

 necessary to detect this connection. 



The most striking and persistent feature of the parabasals is their 

 uniform parallelism. This appears in both the free and encysted stages 

 and in mitosis when daughter parabasals are formed by longitudinal 

 splitting. It is an expression of the bilaterality of the organism which 

 manifests itself in the mutual relations of the elements of this pair of 

 organelles, though the pair itself may lie in a great variety of positions 

 in the body, in but few of which do its members exhibit the definite 

 right-left position of the other organs. 



Tlie parabasals stain uniformly in varj'ing tones of black in iron- 

 haematoxylin and resist destaining quite as much as the karyosome. 



