1919] Kofoid-Sicicu: Strchloniasfi.c stri.r 11 



Unfortunately our material, though extensive, has not given us 

 all of the stages of nuclear behavior during fission so that we are 

 unable to trace wholly, the successive phases of mitosis. We have 

 found no clear evidence of chromosome formation, beyond the twenty- 

 five or more spherical aggregates of chromatin in the linear nucleus. 

 We have found no spherical stage of the nucleus, no skein, and have 

 not detected the division of the blepharoplast which doubtless occurs, 

 neither have we been able to find the paradesmose spun out between 

 the daughter blepharoplasts (pi. 2, figs. 12, 13). 



The process of binary fission, in so far as our partial evidence 

 goes, takes place without any. rounding-up of the elongated body. 

 The anteriorly located blepharoplast divides, new flagella ai'ise from 

 one or both of the daughters, and one migrates to the opposite end 

 of the body (pi. 2, fig. 11). In the meantime the nucleus has become 

 greatly elongated, reaching fi-om end to end of the body. It then 

 constricts at the middle (pi. 2, fig. 12), finally parts there (pi. 2, 

 fig. 19^ and the two schizonts separate. To all appearances this is 

 transverse division. Longitudinal division is, however, the funda- 

 mental and universal method of binary fission in the Euflagellata as 

 compared with the Ciliata in which transverse division occurs. This 

 seeming departure from the normal is, however, more apparent than 

 real, for if the anterior blepharoplast divides and one daughter 

 migrates to the posterior end we will have such an arrangement of schi- 

 zonts as in Trichomonas after mitosis but before plasmotomy (Kofoid 

 and Swezy, 1915, pi. 4, fig. 39). This is a temporary relation in such 

 a metabolic form as Trichomonas but a more lasting one in Strcblo- 

 mastix. The mode of division is therefore still morphologically longi- 

 tudinal though almost the last vestige of the appearance of that type 

 of division has been submerged by the dominating elongation of the 

 body in Streblomastix. While it is possible that there is a series of 

 skein-chromosome changes in the nucleus which has escaped us, our 

 present evidence indicates that these are also suppressed or hidden 

 in the dense chromatin threads which part by simple median constric- 

 tion (pi. 2, fig. 12). This parting is delayed until the posterior 

 daughter blepharoplast is in its final position, as in other polymasti- 

 gotes (Kofoid and Swezy, 1915). The frequent occurrence of stages 

 in schizogony with the nucleus as yet luidivided or dividing, but the 

 neuromotor organelles in duplicate, indicates that both nuclear con- 

 striction and plasmotomy following thereon are .prolonged processes. 



