10 ViiicrrsitiJ of California Puhlications in Zoologij [ \'ol. £0 



Nucleus 



The nucleus (fig. A, n.) isliares the elongation which affects the 

 body and appears to be pulled far anterior by the holdfast function 

 of the blepharoplast so that in comparison with other polymastigotes 

 its location is exceptionally far anterior. Its length is from 0.3 to 0.5 

 that of the body itself and its shape is fusiform but much more slender 

 than the body, its length being fifteen to twenty-five times its diameter. 

 It tapers about equally at both ends and appears in most of our 

 preparations as a solid black axial strand in the anterior part of the 

 body. Unless very strongly decolorized no internal structures can 

 be made out. It appears to be composed of almost solid chromatin. 

 When sufficiently decolorized (pi. 1, figs. 7, 9) a distinct nuclear 

 membrane is evident within which a single I'ow of black chromatin 

 spherules, decreasing in size towards each end, can be detected. These 

 are not uniform in size or arrangement and are about twenty -five in 

 number. They are not unlike the chromomeres which we have found 

 in the chromosomes of Trichomjmpha. 



BINARY FISSION 



The life history of t^treblomastix presents those phases of develop- 

 ment which we (Kofoid and Swezy, 1915 and Kofoid and Christiansen, 

 .1915) have previously described for other polymastigotes, namely, 

 binary and multiple fission. As yet no encystment has been detected 

 and zio indications of sexual reproduction. The differences in size 

 which we find would doubtless some years ago have afforded a basis 

 for the speculative designation of microgametes and maerogametes 

 and the corresponding gametocytes as well as for the predication of 

 sex, as Hartmann (1910) did in the case of Trichonympha. However, 

 in the absence of evidence of sexual behavior and observed fusion of 

 gametic nuclei, the free swing of such speculation is wisely held in 

 abeyance. 



Binary fission occurs in the trophozoite stage. There is some 

 evidence that it is cyclic since many individuals in approximately 

 the same stage of mitosis will be found in a single host. It is not, 

 however, restricted wholly to such cycles since isolated cases of fission 

 have been found and not all individuals parasitic in one host are in 

 fission at one time. Successive infections and diverse stocks of the 

 parasites doubtless exist in the host and may afford the occasion for 

 this diversity. 



