KARYOKINESIS AND ITS RELATION TO FERTILIZATION. 197 
Division of the nucleus takes place in the way which we 
have so far been describing, or as it is carried out in the seg- 
mentation of the egg, i.e. the nucleus divides either in an 
equatorial plane or in the meridian (segmental plane), and the 
products of division which are usually exactly equal separate 
with an even surface; this is ‘‘ segmentation.” This is “in- 
direct ” if it is accompanied by karyokinetic appearances, 
otherwise it is“ direct.” In -‘ fragmentation” (which word 
was originally applied by EH. van Beneden to ordinary direct 
division, and by Strasburger was used for “nuclear disinte- 
gration”), the surface of separation of the daughter nuclei 
is quite uneven; portions are nipped off from the outside 
with irregular surface of separation, or may separate on the 
inside, and remain connected for a long time, by a bridge, 
with the mother-nucleus. In this case the portions into 
which the nucleus divides are not necessarily unequal in size, 
although they usually are. Here also karyokinetic appear- 
ances may be present (‘indirect fragmentation”), or absent 
(“direct fragmentation”). When karyokinetic figures are 
found in fragmentation, they show themselves by an increase of 
chromatic substance, and by the appearance of chromatic loops 
and of granules in greater distinction and number; in all 
instances there is, however, in the case of “ fragmentation ” 
no indication of an equatorial arrangement, and in this consists 
the essential difference between fragmentation and segmenta- 
tion. Further differences are shown in the more varying and 
irregular form of the chromosomes, which may appear as 
granules, threads, or bands. Arnold frequently found a band- 
like form of chromosome in the spleen. Again, the disposition 
of the chromosomes is irregular, not infrequently the polar 
arrangement is absent. Arnold leaves it undecided whether 
the typical longitudinal splitting always takes place. The 
nuclear membrane remains for a long time, and even in the 
earliest phases constrictions of the nucleus are observed. 
As can be seen, fragmentation amounts essentially to a 
process of budding, as Arnold’s drawings show. That this 
abnormal form of division, which results in a process of 
