162 University of California Publications in Zoology [Vol. 19 



crithidia. The results of the study now indicate that the extranuclear 

 organelles are apparently formed as outgrowths from the nucleus. 

 It is conceived that the centrosome of the nucleus divides, giving rise 

 to the extranuclear centrosome, or blepharoplast. Prom the blepharo- 

 plast, which is the dynamic center of the nuclear outgrowth, two 

 other organelles are formed. The flagellum grows forward anteriorly 

 and the parabasal body to the side. The connection which persists 

 between the blepharoplast and the nucleus is the nuclear rhizoplast. 

 Between the blepharoplast and the parabasal body is the parabasal 

 rhizoplast. Careful observation of some of the larger forms reveals 

 a cytoplasmic sheath around the flagellum, which is continuous with 

 a similar sheath around the parabasal body. The latter sheath is 

 like a sack, in which the deeply staining, bar-shaped parabasal body 

 is suspended. The variation in size of the parabasal body may 

 explain the light area which is frequently observed to surround this 

 organelle. The fan-shaped appearance of the parabasal rhizoplast 

 is due in all probability to this sacklike sheath. Any general con- 

 clusions concerning the origin of these organelles would, at this time 

 however, be premature, although the observations of the zooids under 

 the binocular microscope tend to give this conception of their origin. 

 It is necessary to keep in mind constantly the fact that the material 

 with which we are dealing is the complex life cycle of a flagellate and 

 that several stages of the life cycle have not yet been followed, step 

 by step, in the living material. The possibility of confusing two life 

 cycles is always present, and the fact that all of the w T ork is done 

 near the limits of microscopical magnification adds further possibility 

 of misconception. 



Aside from these difficulties and doubtful points, however, the 

 discovery of all of these stages of what has been interpretated as a 

 process of endogenous budding, opens up further problems for investi- 

 gation in the life cycles of these flagellates. The origin of the para- 

 basal body in the endogenous bud is a big problem in itself. In addi- 

 tion, the light thrown upon the probable origin of the numerous 

 binucleated spores or Leishmania-like bodies, which occur so abun- 

 dantly in the life cycles of such flagellates as Schizotrypanum cruzi 

 (Chagas, 1910), Crithidia melophagia (Porter, 1910), and C. lepto- 

 coridis (McCulloch, 1915), is very suggestive. 



Somatella. — Previous to the discovery of the multinucleated flag- 

 ellates which were undergoing a process of internal or endogenous 

 budding, another type of multiple fission had been studied in prepara- 





