1906] OLIVE—NUCLEAR AND CELL DIVISION OF EMPUSA 247 
that this equal division of the chromatin occurs somewhere in the 
obscure prophases; in Empusa, e. g., probably long before the appear- 
ance of the conspicuous centers seen in jig. 50. 
The absence of the arrangement of the chromatin into an 
equatorial plate prior to the divergence of the two daughter masses 
possibly results from the poor development of the achromatic -spin- 
dle, due to the small amount of linin present in the nucleus. To 
this same cause is probably due also the failure to form definite chro- 
mosomes in these simple organisms. In Amoeba, according to 
SCHAUDINN’s observations (’94), there are apparently no radially 
arranged chromatic filaments; while in Coccidium (SCHAUDINN, : 00) 
and Empusa, evidently a still higher type obtains, since in both these 
instances we have formed, rather late in division, filaments of chro- 
matin, which undoubtedly correspond to the chromosomes, and are 
radially arranged about the centrosomes. 
The formation of an “equatorial ring” in the nuclear division in 
Euglena, and of a more compact equatorial arrangement of the chro- 
matin in Euglypha (ScHewiakorr, ’88), Actinospherium (HERT- 
WIG, ’98), Paramoecium (HERTWIG ’95), Aulocantha (BoRGERT, :00), 
and other Protozoa, certainly indicates the presence in these forms 
of a more highly differentiated mechanism for the halving of the 
chromatin. In all these cases, we note the early formation of 
chromosomes, which are usually very clearly defined, and generally 
a well developed spindle, consisting of both central spindle as well 
as polar mantle-fibers; so that we are justified in the conclusion that 
in these more highly differentiated figures there is a greater amount 
of intranuclear achromatic substance present than in the nuclei of 
Empusa and Coccidium. 
We may compare at this point the degree of differentiation of the 
intranuclear spindle in these organisms. KEUTEN regards the dumb- 
bell shaped nucleolo-centrosome in Euglena as probably serving as 
a spindle mechanism; and Boveri (:00) and CALKINS (:01,:03) also 
think that the strand of connecting substance in this constricted 
nuclear body corresponds to the central spindle of higher organisms. 
CALKINS (: 01, p. 265) points out in this connection that Paramoecium 
furnishes a clew to the relationship of such connecting strands in 
Euglena to the fibrillated central spindle, since in Paramoecium the 
