1919] Rhodes: Binary Fission in Collodictyon triciliatum Carter 233 



two tubercles protrude. From each granule two equal flagella arise. 

 Two faint rhizoplasts join the blepharoplast to the nucleus and 

 karyosome. At the points of contact of the rhizoplasts with the 

 nuclear membrane, very small granules are found, which function as 

 extranuclear centrosomes. 



6. The typical vesicular nucleus undergoes a true mitosis of a 

 type probably related to mesomitosis. 



7. There is an unequal constriction and differential division of 

 the initial karyosome, the resulting karyosomes being designated 

 macrokaryosomes and microkaryosomes. 



8. A kinetic membrane is organized around the microkaryosome 

 and during the prophase expands until it apparently becomes com- 

 mensurate with the nuclear membrane. 



9. The macrokaryosome rounds up in a niche of the nuclear mem- 

 brane, not being involved in mitosis. Its possible fate and significance 

 will be discussed in the latter part of this thesis. 



10. The nuclear membrane is persistent during mitosis. 



11. There is evidence for an extranuclear centrosome, such as has 

 been found in parasitic flagellates, but in this instance it is separated 

 from the blepharoplast and connected with the same by rhizoplasts. 

 Further work on this and other free living flagellates is much needed 

 to more clearly demonstrate this and related problems. 



12. There is an intranuclear chromatin cloud during the prophase. 

 In the final prophase, the anaphase and telophase an extranuclear 

 chromidial cloud is also formed. 



13. The microkaryosome organizes within the kinetic membrane, 

 apparently separates into two masses connected by fibers and may 

 pass through a tripod and ring stage. This passes into a double 

 segmented spireme stage, in which there are four terminal chromatin 

 masses or knobs. 



14. A separation of this spireme takes place, the resulting terminal 

 masses, seven or eight, forming the chromosomes. There is a pre- 

 cocious splitting of the peripheral chromatin granules. 



15; In the final prophase when the segmented skein is arranged 

 about the equatorial plate, there is a precocious splitting of the 

 chromatin masses, which may be indicative of the division and dis- 

 tribution of the chromosomes which is about to take place. In this 

 way the transverse division of the chromosomes may be explained as 

 a fundamental longitudinal division, as determined by this precocious 

 splitting. 



