234 University of California Publications in Zoology [Vol. 19 



16. The number of chromosomes is seven or eight, which in meta- 

 phase are arranged on the equatorial plate of a perfect spindle. 



17. The chromosomes part transversely. In the only satisfactory 

 metaphase observed (pi. 12, fig. 50) one lags on the spindle. 



18. The resulting chromatin masses in early anaphase are some- 

 times unequal in size, but this is soon concealed by a rapid growth of 

 chromatin in the later anaphase and telophase. 



19. The reorganization of a typical skein, which breaks up into 

 chromatin masses, some of which go to form the karyosome, some the 

 peripheral chromatin, and some may be extruded. 



20. The basal granules separate, the flagella split longitudinally 

 or grow out anew, the rhizoplasts split from the nuclear end, and the 

 two resulting blepharoplasts contain two new basal granules from 

 division of one of the old, inherited from the old blepharoplast, and 

 are connected with four equal flagella and a rhizoplast. 



21. A paradesmose typical of polymastigotes in general is present 

 between the separating centrosomes, on the nuclear membrane. 



22. Final separation of the cells takes place in the plane of the 

 sulcus, parallel with the major axis of the cell, by the rupture of one 

 or more of the vacuoles of the constricted protoplasmic connection. 



DISCUSSION 



Classification and Relationship 



Prowazek (1903a.) attempted to classify the nuclei of Flagellata, 

 distinguishing four different types, which Dobell (1908) has summed 

 up: 



1. Simple nuclei, with an evenly distributed chromatic network, and no 

 internal structures (karyosome, division centre, etc.), e.g., Herpetomonas. 



2. Vesicular nuclei, with direct division; with central chromatin mass sur- 

 rounded by a clear zone, across which a more or less distinct network extends 

 outward to the nuclear membrane. Such a nucleus may be seen in some species 

 of Bodo, and is well seen in Copromonas. 



3. Centronuclei containing a "nucleolo-centrosome" (Keuten, 1895) and 

 separate chromatin masses. This type of nucleus is characteristic of Euglena 

 and its allies. (The centro-nucleus, as defined by Boveri, is a nucleus which 

 contains a cyto-centre, either in a consolidated or diffuse form. In the case of 

 Euglena, etc., the cyto-centre is the nucleolo-centrosome, i.e., is of the con- 

 solidated type.) 



4. Vesicular nuclei with karyokinetic division: e.g., Polytoma, Chlamydo- 

 monas, etc. 



