21-t University of California I'uhliraiions in Zoologi/ [Vol. Ifi 



of the flagellurn, blepharoplast, rhizoplast, parabasal body, and 

 nucleus, in these figures become exactly comparable with those shown 

 for Pohjmastix bufonis (fig. 47) and Trichomonas augusta (fig. 58), 

 in that a direct connection is established between the blepharoplast 

 and nucleus, while the parabasal body occupies the position of an 

 accessory organelle connected with the blepharoplast at one side, in- 

 stead of in the direct line of structure from flagellurn to nucleus ; that 

 is, it is in precisely the relation of the parabasal body. This relation- 

 ship would suggest a function as an accessory organelle for the para- 

 basal body, in opposition to the view which would give to it the posi- 

 tion of the kinetic center, or kinetonucleus, of the cell. This relation- 

 ship would also militate against the idea of its origin by a heteropole 

 division of the nucleus. 



The transition from Herpetomonas to Crithidia has been made by 

 a backward migration of the blepharoplast with its attendant para- 

 basal body and flagellurn to the middle regions of the cell. This back- 

 ward migration is followed, in the evolution of the trypan osomes, by a 

 still further backward migration of this structure until the posterior 

 region of the body is reached, with a corresponding development of an 

 undulating membrane. 



The relations of the neuromotor apparatus of the trypanosomes, 

 consisting of the same organelles as found in Crithidia, are, at least 

 in some stages of its life-cycle (fig. 7), the same as has been pointed 

 out above for that genus {cf. Kofoid, 1916). 



This condition found in the trypanosomes represents the highest 

 stage of development reached by the Crithidia line of evolution of 

 extra-nuclear organelles. That this is the probable course of evolu- 

 tion is shown by the fact that these stages, herpetomonad and crithi- 

 dial, both occur in the life-cycle of the highest member of that group, 

 Tr.ypanosoma (Minchin and Thompson, 1915). 



To conclude : It has been shown in the preceding paragraphs, that 

 the only actual occurence of the formation de novo of the blepharo- 

 plast is found in some of the primitive amoebas, in which a granule 

 is budded ofi' from the karyosome of the nucleus and migrates to the 

 periphery of the cell where it gives rise to the flagella. This granule is 

 not the centriole but may possibly be formed by a division of that 

 body. The development of the neuromotor apparatus of the trypano- 

 somes is found in two of its earlier stages in Herpetomonas and Cri- 

 thidia. The relations of the parabasal body in Crithidia suggest that 

 found in Polyniasti.v bufonis and Trichomonas augusta, and also sug- 



