314 Wisconsin Academy of Sciences, Arts, and Letters. 
and suggests that there may be several races of this species differ¬ 
ing in the number of chromosomes. 
Resume 
1. The resting nucleus does not in general contain a continuous 
reticulum. Elementary alveolar-reticulate bands which represent 
the chromosomes can be distinguished, often forming lobes in the 
nucleus. 
2. No karyosomes or prochromosomes are present in the rest¬ 
ing nucleus. 
3. During prophases the alveolar-reticulate chromosomes con¬ 
dense to form zigzag threads which later thicken and shorten. 
4. These thin threads split longitudinally, probably by means 
of axial vacuolation, the split persisting until the chromosomes are 
separated at metaphase. 
5. No continuous spirem is present at any time. 
6. Evidence exists that the chromosomes consist of two sub¬ 
stances, linin and chromatin, the latter often appearing in the 
form of definite chromomeres. 
7. The chromosomes are arranged on the spindle with their 
halves superposed. Spindle fibers may be attached at any point 
to the chromosomes. 
8. The chromosomes show a tendency to be arranged in homol¬ 
ogous pairs on the spindle. A similar arrangement can not al¬ 
ways be seen during rest, but strong evidence is often found of 
such pairing during the prophases. 
9. There is no massing at the poles of the telophasic chromo¬ 
somes, each chromosome remaining separated from its neighbors. 
10. The telophasic chromosomes are not normally connected 
by cross anastomoses. 
11. Each chromosome undergoes an irregular alveolation, the 
beginnings of which become slightly evident as early as the meta¬ 
phases, but the alveolation continues to increase through the ana¬ 
phases and telophases until each chromosome by complete vacuo¬ 
lation forms an alveolar-reticulate structure of the resting reti¬ 
culum. 
12. Each chromosome for a time is apparently surrounded by 
its own membrane, thus resembling a karyomere. The chromo¬ 
some membrane apparently enters into the formation of the nu¬ 
clear membrane. During rest the chromosome membrane is broken 
