1919] Rhodes: Binary Fission in Collodictyon triciliatum Carter 225 



peripheral granular area to the nuclear membrane; from here they 

 pass through the intervening cytoplasm to the basal granules within 

 the blepharoplast. The rhizoplasts are not sufficiently prominent to 

 be evident to the uninitated eye. They may easily be confused with 

 the attenuated strands from the blepharoplasts radiating out into the 

 surface cytoplasm. 



Two small granules have been observed just at the point where 

 the rhizoplasts enter the nuclear membrane on their way to the central 

 karyosome (pi. 8, figs. 9, 13). In early and late prophase stages 

 (pi. 14, fig. 75) these separate and the nuclear membrane appears 

 heavier or thicker between these points in comparison with the rest 

 of the membrane, as though an extranuclear paradesmose were form- 

 ing. In a lately discovered metaphase (pi. 14, fig. 78) this paradesmose 

 is well formed, connecting the polar ends of the spindle. In one 

 particularly favorable anaphase (pi. 14, fig. 83) granules of consider- 

 able size are located at the polar ends of the daughter chromatin 

 masses and these are connected by a heavy paradesmose upon the 

 nuclear wall. 



This evidence points definitely to the presence of an extranuclear 

 division center or centrosome. Such is typical of parasitic poly- 

 mastigotes (Kofoid and Christiansen, 1915, Kofoid and Swezy, 1915a, 

 1915&, Swezy, 1915, Boeck, 1917) and may be considered typical of 

 polymastigotes in general. In this case, however, the blepharoplast 

 and centrosome are separate, the latter adhering to the nuclear 

 membrane. 



The rhizoplasts split first at the end near the nuclear membrane, 

 presumably with the division and separation of the centrosomes. The 

 split extends anteriorly, giving the appearance of a V-shaped striated 

 region (pi. 8, fig. 13). Finally with the separation and division of 

 the basal granules of the blepharoplast (pi. 8, fig. 9) the rhizoplasts 

 appear distinct and their points of contact with the nuclear mem- 

 brane become farther apart. 



In justice to truth, it must be said that the problem of the division 

 center has been full of difficulties. The material in hand is of such 

 a nature that the possibility of error must not be overlooked. The 

 apparent points of contact of the rhizoplast with the nuclear mem- 

 brane are exceedingly faint. The extranuclear cytoplasmic granules 

 and vacuoles and the intranuclear chromatin encrusted in granules 

 upon the nuclear membrane, which are connected in prophase by 

 somewhat chromatic lines, are exceedingly confusing. This renders 



