The nuelear components of the sex eells of four species of cockroaehes. 497 
the earliest prophase (fig. 36), the ordinary chromosomes appear in 
the form of delicate threads ramifying through the nucleus. These 
threads gradually thicken (fig. 37) and the ends of the threads become 
marked by conspicuous knobs which, even in the earlier Kondition, 
may be seen to be double. The threads themselves do not appear 
to be double during the earlier stages but soon this condition is 
apparent as the bodies shorten and thicken (fig. 38 . It will be seen 
here that the space between the knobs is continuous with that 
running longitudinally through the whole chromosome. Shortening 
and thickening continues (fig. 39) and the chromatin bodies become 
similar in appearance to the chromosomes of the metaphase plate. 
The knobs are still conspicuous, but the body of each chromosome 
has become so short that the knobs at either end of the chromosome 
are almost in apposition (fig. 39j, giving a quadripartite appearance 
to the chromosomes. The centrosomes divide about this time (fig. 39; 
the centrosomes iie, of course, outside of the nuelear membrane, but 
they have been projected here and appear to be inside of the nu- 
cleus; figure 48 shows their true position). It is difficult to distinguish, 
during these stages the longitudinal division of the chromosomes, but 
when they are oriented on the spindle (fig. 41) the split becomes 
more evident. As the chromosomes enter the metaphase plate (fig. 41). 
a change in their appearance occurs, the quadripartite appearance 
gives way to a dumb-bell form, the contraction of the bell representing 
the position of the split separating the daughter chromosomes. This 
dumb-bell shape arises by the knobs of the daughter chromosomes 
becoming verv closely applied to one another. Sometimes the space 
between them can be seen, but it is faint and elusive. The chromo- 
somes arrange themselves regularly in the metaphase plate (fig. 43) 
and divide synchronously (fig. 44), thus differing conspicuously from 
the corresponding stage of the first spermatocyte division. In the 
telophase, they soon break down into a network (fig. 45) and become 
indistinguishable as separate chromosomes. The number of chromo- 
somes^ in the second division will be spoken of under the odd chro- 
mosome. 
b) The odd chromosome. In the early prophase of the second 
division (fig. 36), a conspicuous chromosome-nucleolus is present 
in which a longitudinal split is faintly visible even in the earliest 
stages, immediately after the telophase of the preceding division. The 
characteristic pear shape of the earlier stages is also shown at this 
time. Its staiuing capacity increases about the time the threads, re- 
' 33* 
