308 KOFOID AND SWEZY. 



the total length, is enlarged to 1.2-3 times its diameter in the shaft 

 which is of nearly uniform caliber, though it tapers gradually in some 

 cases (PI. 1, Fig. 1), may enlarge at the point of emergence (PI. 1, 

 Fig. 10), or may be constricted near its middle and enlarged again 

 distally (PI. 1, Fig. 7). Its diameter in the enlarged capitulum is 

 0.12-0.07 of its length, and in the shaft 0.02-0.045. Its distal end 

 in the normal free-swimming forms (PI. 1, Fig. 3) is exposed for about 

 0.2 of its length but extent of this decreases in the mitotic period 

 (PI. 2, Figs. 11-19) even to complete inclusion in the cytoplasm, and 

 in cases of posterior blob formation (PI. 1, Fig. 2, and Fig. C, G-8) 

 the distal end may be some distance within its margin. This end is 

 attenuate to a sharp point, but often somewhat abruptly as in a 

 pencil. 



The axial position of the axostyle gives to it a nearly straight form 

 in most vegetative stages. Its enlarged capitulum pushes aside the 

 nucleus, abuts immediately upon the dorsal side of the cytostome and 

 at its apex is attached to the blepharoplast (PI. 1, Fig. 1) which in 

 some instances (PL 1, Fig. 2) even indents this region. This axial 

 organ, however, is very frequently curved with the convexity parallel 

 to that of the chromatic basal rod and undulating membrane (PI. 1, 

 Fig. 1). This is especially noticeable in individuals which are rounding 

 up (PI. 1, Fig. 8). A comparison of the Figures on Plates 1 and 2 

 shows at once that the axostyle cannot be considered as a rigid fixed 

 structure but rather as one subject to a high degree of mobility, or at 

 least of flexibility. 



The body of the axostyle consists of homoii :neous hyaline sub- 

 stance which shows no internal fibrillar structure, has a more or less 

 sharply defined periphery, and contains from 15-90 deeply staining 

 chromatin granules or axostylar chromidia {ax. chr., Fig. B). These 

 are generally less numerous in the vegetative phase and more so prior 

 to division. There is a very considerable variation in numbers in 

 approximately similar stages (PI. 2, Figs. 16, 18). These granules 

 are 0.3-0.5 micron in diameter, generally spheroidal, and tend to be 

 equidistant from each other in distribution as though under mutual 

 repulsion. They are most numerous anteriorlj^ in the capitulum of 

 the axostyle and when but few are present (Pi. 1, Fig. 3) they are 

 restricted to this region. As they become more numerous they extend 

 distally to the level of emergence of the axostyle from the cytoplasm, 

 but we have never found them beyond this level. In a number of 

 instances one, two, or three pairs of posterior axostylar granules 

 (post. ax. gr., Fig. B) lie (PI. 1, Figs. 1, 5, 7) in the cytoplasm or in the 



