104 C. CLIFFORD DOBELI. 
the nucleus, flagellum, and basal granule—three structures 
which are probably connected phylogenetically. 
Prowazek (86) distinguishes four different types of nucleus 
among the Flagellata : 
(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 surrounded by a clear zone, across which a 
more or less distinct network extends outwards to the nuclear 
membrane. Such a nucleus may be seen in. some species 
of Bodo, and is well seen in Copromonas. 
(3) Centro-nuclei! containing a ‘‘ neucleolo-centrosome ”’ 
(Keuten) and separate chromatin masses. This type of 
nucleus is characteristic of Huglena and its allies. 
(4) Vesicular nuclei with karyokinetic division: e.g. 
Polytoma, Chlamydomonas, etc. 
To these four categories we may make the addition of a 
fifth, for the reception of the kind of nucleus found in 
Tetramitus (Calkins [7]). 
(5) Nuclei in which the achromatic division-centre lies 
freely in the cell, whilst the chromatin is diffuse in the form 
of chromidia. ; 
The nuclei will be seen to be of very different structure 
throughout the group. This difference is no less marked in 
the method of division. All stages, from amitotic constric- 
tion into two to karyokinesis with chromosomes, achromatic 
spindle and division-centres are to be met. 
Fisch (19) described mitosis in Codosiga in 1885. In 
1894 Blochmann recorded its occurrence in Polytoma and 
Monas vivipara (2) andin Euglena (8). His pupil Keuten 
carefully worked out the nuclear division in this last form in 
1895 (25), describing the nucleolo-centrosome and a longitu- 
dinal splitting of the chromosomes. Schaudinn next year 
1 The centronucleus, as defined by Boveri, is a nucleus which contains a 
eytocentre—either in a consolidated or diffuse form. In the case of Euglena, 
etc., the cytocentre is the neucleolo-centrosome, i.e. is of the consolidated type. 
