164 University of California Publications in Zoology [VOL. 19 



division of the blepharoplast, the parabasal body, and the nucleus 

 has occurred. A second flagellum growing out from the daughter- 

 blepharoplast cannot be observed. Another more advanced stage of 

 multiple fission is shown in the somatella in figure 27. The number of 

 nuclei and of the parabasal bodies is the same as in figure 26, but the 

 outgrowths of the daughter-flagella are clearly shown in this sphere. 

 Spheres without protruding flagella are to be found in figures 28 and 

 29, plate 3. The formation of the merozoites within the spheres, as 

 presented in figure 29, has advanced to the point where they are 

 clearly defined. In figure 28 another important observation can be 

 made, namely, that the divisions of the blepharoplast and the nucleus 

 do not occur simultaneously. In this particular sphere there are three 

 parabasal bodies present but only two nuclei. In figure 29 there are 

 four merozoites visible, each of which shows the outgrowth of a flag- 

 ellum, and a similar spherical formation is shown in figure 30, wherein 

 the four merozoites are somewhat larger and more developed. In the 

 latter somatella, however, the thickness of the sphere prevented the 

 usual amount of destaining necessary to show the nuclear structure. 

 In each of these merozoites the body is elongating and the anterior 

 end is becoming attenuate. 



Another thick sphere is found in figure 31, and all the nuclei 

 therein have the appearance of being a solid mass of chromatin. In 

 this somatella the number of merozoites which could be counted is 

 twelve. The irregular outline of the sphere indicates that the breal\- 

 ing up or plasmotomy of the sphere is about to occur. Possibly some 

 of the merozoites have already escaped. In the investigation thus 

 far the number of merozoites in a somatella has been exceedingly 

 variable. In some of the Polymastigina, Kofoid and Swezy (1915) 

 found the number of merozoites to be eight, which is apparently con- 

 stant for the somatellas of these flagellates. Minchin and Thomson 

 (1915) report a variable number of merozoites in the spheres of 

 Trypanosoma lewisi but they found the average number to be approxi- 

 mately ten. In the spherical mass of flagellates shown in figure 31, 

 plate 3, the number is twelve, but in a still larger sphere (pi. 3, fig. 

 32) the number is probably double that, or twenty-four. The dense- 

 ness of the latter may have obscured some of the parabasal bodies and 

 nuclei. Protruding from the surface of this sphere are numerous flag- 

 ella which are outgrowths from the daughter-blepharoplasts. In the 

 somatellas of the Polymastigina the nucleus and the extranuclear 

 organelles may divide simultaneously, but in the spheres of T. leivisi 



