212 Universifij of Calif oniia PuhUcatioiis in Zoologij [Vol. Ki 



It has been claimed by many investigators on these forms that the 

 flagellum arises directly from the parabasal body, or at least that no 

 other granule is connected with it (Prowazek, 1904, Patton, 1908, and 

 others), and many of tlieir figures show only an undifferentiated 

 chromatin mass at the base of the flagellum. This condition would be 

 explained by the probability that the parabasal body was formed as 

 an outgrowth of darkly staining granules from the blepharoplast 

 which was not entirely separated from it in the earlier stages of its 

 formation. 



This view seems more in accord with the facts as shown in the 

 intimate relation of these two structures, in the similarity in their 

 methods of division and in the direct outgrowth of comparable struc- 

 tures in Trichomonas and in some of the Trichonymphida than does 

 the theory which would m.ake the blepharoplast a secondary deriva- 

 tive of the parabasal body, for two reasons. The first reason is that 

 the simple basal granule, or blepharoplast, is the more primitive con- 

 dition, and second, to have the blepharoplast of the trypanosomes take 

 its origin from the parabasal body it would be necessary to suppose 

 that the parabasal body was the original definitive nucleus, or part 

 of it, or else that the original basal granule or blepharoplast was lost 

 and a new one had to be secondarily formed. Neither of these suppo- 

 sitions is supported by the actual facts of mitosis as known at the 

 present time. 



The next stage in the evolution of this structure shows a further 

 development resulting in a parabasal body more or less separated 

 from the blepharoplast, as found in Crithidia. This flagellate pos- 

 sesses a short, often rudimentary, undulating membrane attached to 

 the single flagellum, which arises from a blepharoplast near the pos- 

 terior part of the proximal third of the body (fig. 16). The blepharo- 

 plast, as shown in the recent work of McCulloch (1915), is connected 

 with tlie parabasal body by numerous fine unstained fibers, forming 

 a cone-shaped structure between the two granules (fig. 15). The 

 blepharoplast in these forms is minute and often difficult to demon- 

 strate, as is also the case with the connecting fibrils between it and 

 the parabasal bod.y. In many figures given for Crithidia as well as 

 for the trypanosomes by most investigators, the parabasal body is 

 shown with a clear area between it and the end of the flagellum, evi- 

 dence that the flagellum does not take its origin from that structure. 



The rhizoplast connecting the motor organelles with the nucleus in 

 Crithidia seems, in most cases, to pass through the parabasal body. 



