234 University of California Puhlieations in Zoology [Vol. 16 



E. SUMMARY 



1. The "kinetouucleus" is a structure which, in the trypanosomes 

 at least, is not composed of nuclear chromatin, nor can nuclear be- 

 havior, shown in mitosis, be claimed for it. It is a structure cor- 

 related with an endoparasitic mode of life, and is part of the extra- 

 nuclear motor apparatus, which, in those cases where its origin can 

 be traced, arises from the blepharoplast, and not by a division of th<> 

 nucleus. 



2. The " kinetonueleus " has been developed phylogenetically along 

 two lines: first, from a uniflagellate ancestor possessing a simple basal 

 granule, producing Trypanosoma, Crithidia and Hcrpctomonas; sec- 

 ond, from a heteromastigote ancestor, also exliibiting only a simple 

 basal granule, along the line of Prowazekia. Polymasti.r. Trichomonas. 

 and the Trichonymphida. 



3. The chromidial body of Prowattkia arises as an outgrowth from 

 a simple basal granule. Different stages in its development can be 

 traced from this condition to the "kinetonueleus" of P. cruzi, fol- 

 lowed by its backward migration to a position posterior to the nucleus. 

 The various forms which it assumes are all different aspects of the 

 same structure, morphologically and functionally equivalent to the 

 "kinetonueleus" of the trypanosomes. 



4. The next stage in the development of the "kinetonueleus" has 

 produced, by a course of parallel evolution along two different lines, 

 organelles in Polymastix and Trypanoplasma similar in their mor- 

 phology and behavior in division. These are accessory kinetic struc- 

 tures comparable to the ' ' kinetonuclei ' ' of the haemoflagellates. 



5. A slight modification of the long, band-like "kinetonueleus" of 

 Prowazekia lacertae is found in the chromatic basal rod of Tricho- 

 monas. This is an accessory structure intimately related to the 

 blepharoplast and the entire neixro-motor apparatus and probably 

 kinetic in its function, and hence an organelle homologous with 

 the "kinetonueleus" of the trypanosomes. 



6. A further development of the "kinetonueleus" is found in the 

 parabasal bodies of the Trichonymphida, a group pliylogenetically 

 close to Trichomonas. These bodies are accessory kinetic structures 

 and in every respect comparable with the same organelles found in 

 the other flagellates. 



