1916] Sirezi): KiiictonKclnis of FlagcUates 211 



Flagellates are frequently found in which the flagelluni with its 

 blepharoplast is connected with the karyosome by a rhizoplast. It is 

 found among the simpler as well as the more specialized flagellates and 

 is probably the earliest form of flagellar insertion, a supposition to- 

 wards which the conditions in the amoeba also point, as it is here a 

 new formation in an amoeboid organism. 



The origin of the blepharoplast in the centriole or karyosome of 

 the amoeba may throw some light upon its function as the centrosome 

 in the dividing flagellate. In many species of amoeba the division of 

 the centriole to form the karyosome of the dividing nucleus is fol- 

 lowed by division or elongation of the karyosome or a part of it to 

 form the large "poleplates" of the spindle (Aragao, 1909, pi. 2, figs. 

 3-7, 13-18), the whole structure, apparently, performing the func- 

 tions of the centrosome. 



In all cases in which division of flagellates has been carefully 

 worked out, it has been found generally that the process is initiated 

 by a splitting of the blepharoplast. The blepharoplast thus forms a 

 division center for the cell, even where an additional definitive centro- 

 some for the nucleus is present. This function, then, combined with 

 its position as the basal granule of the flagellum, constitutes it a 

 blepharoplast as that organelle has been defined by Webber (1897!i, 

 and this name will be used for it in the following discussion. 



In the evolutionary development of the parabasal body, its mor(^ 

 primitive form may be looked for among the simpler parasitic flagel- 

 lates, the herpetomonads, as in these forms the change from the ordi- 

 nary cercomonad type is but slight. In Herpetomonas (fig. 8) the 

 primitively single flagellum arises at the anterior end of the body 

 from a blepliaroplast which is in turn connected with the parabasal 

 body (Weuyon, 1913). The parabasal body here consists of a mass 

 of deeply staining material which, in the majority of forms, shows 

 but slight, if any, structural difi'erentiation. The simple blepharo- 

 plast attached to the nuclear membrane in Cercomonas (Wenyon, 

 1910), has presumably migrated some distance from it in Herpeto- 

 monas, and formed the parabasal body by a secondary outgrowth 

 from itself, between itself and the nucleus. Actual evidence in sup- 

 port of this last proposition has not been found among the herpeto- 

 monads, but it will be shown below that this process actually takes 

 place in Prowazekia, and, by analogy, we would expect the same con- 

 ditions to obtain here. 



