MITOSIS AND CELL DIVISION IN EUGLENA. 113 



anteriorly until it finally divides the reservoir into halves (Figs. 

 9, 10, n). When this is completed the anterior end of the or- 

 ganism widens so that the mouths of the two reservoirs become 

 separated (Fig. n); then division of the body begins at the 

 anterior end proceeding posteriorly in a line between two cuticular 

 striations (Figs. 12, 13). The body and body contents are thus 

 divided into two approximately equal parts (Fig. 14). 



6. Reorganisation. Following cell division the organism under- 

 goes very little change for some time. The nucleus remains at- 

 tached to the belpharoplasts (Fig. 14) as it slowly moves posteri- 

 orly. The chromatin becomes less condensed slowly assuming the 

 appearance of the vegetative stage. The endosome buds off a 

 portion of its substance to form the intranuclear body (Fig. 14) 

 which remains unchanged until the succeeding mitotic division, 

 and the central vacuole reappears, small at first (Fig. 14) grad- 

 ually becoming larger until the usual size is reached. 



III. DISCUSSION. 



1. Division Center. This study of the mitosis of E. spirogyra 

 sheds little light upon the problem of the division center or cen- 

 triole of the free-living flagellates. The mitotic process takes 

 places within the nuclear membrane and if any structure, present 

 at this time, is comparable to the division center of other forms, it 

 is the endosome. The structure may also be comparable to the 

 spindle and centrosomes of higher types but nothing has been 

 found that would convince one that it contains a division center. 



2. Chromosome formation and division in E. spirogyra is quite 

 similar to that of metazoan types. The chromosomes form, in 

 the prophase, from the paired strands of chromomeres into paired 

 chromosomes of the metaphase, which separate and undergo a 

 longitudinal fission in the following anaphase. In the daughter 

 nuclei, during the telophase, they resolve into the vegetative state 

 in which they are arranged as paired rows of granules or chromo- 

 meres. Thus for this form at least we have an example of 

 mitosis in the protozoa that bears out " one of the most funda- 

 mental conceptions of cytology and genetics, namely, that the 

 spireme threads are linear aggregates of much smaller self-per- 

 petuating bodies, aligned in single series and definite order ' 



