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University of Califoniia Publicnfions in Zooloyii [Vol. 16 



Hypotheses coucei'uiug the phylogeuetie origin of parasitic forms 

 must of necessity be mere guess-work, at the present time at any rate. 

 It is quite certain that they arose from organisms not very unlike the 

 present species of free-living Protozoa. Adaptation to a parasitic 

 mode of life, taking place in a number of genera, might well be sup- 

 posed to lead to the present conditions, where a number of parasitic 

 species exhibit organelles which are homologous in structure and ana- 

 logous in apparent function, or are at least convergent. This is ana- 

 logous to what takes place in specialization throughout the animal 

 kingdom and is a condition which would naturally be expected to 

 occur here also. That such a condition does occur in this group, I hope 

 to be able to show in the following pages, in evidence pointing to the 

 homology of the parabasal body of the trypanosomes \\ith the so- 



Fig. 7. Schisotrypauum cruzi Chagas, after Chagas (1909, pi. 9, fig. 13). 

 Trophozoite showing nucleus, parabasal body, blepharoplast, undulating mem- 

 brane and flagellum; note fibrils connecting blepharoplast with parabasal body. 



Fig. 8. Herpetomonas muscae domesticae (Burnett), X 2500. Trophozoite 

 showing nucleus, parabasal body, blepharoplast and flagellum. 



Figs. 9-10. Trypanoplasma carassii sp. nov. Fig. 9. Trophozoite, showing 

 nucleus, parabasal body, blepharoplast, undulating membrane and flagellum. 

 Fig. 10. The same. 



called chromidial body of Prowazekia and Polymastix, the chromatic 

 basal rod of Trichomonas and the parabasal bodies of the Trichonym- 

 phidae, structures which are correlated with an endoparasitic mode 

 of life and are intimately related to the motor apparatus. 



Two lines of development of the parabasal body may be noted here, 

 the first springing from a uniflagellate ancestor and finally resulting 



