CHROMOSOMES 249 
into which the thread eventually breaks up. The 
thread gradually grows shorter and thicker, and 
presently becomes divided into a number of pieces 
which are known as chromosomes. In the chromo- 
somes the shortening and thickening process is con- 
tinued until these bodies arrive finally at the form of 
stumpy rods, each of which often becomes bent into 
FIG. 19. FIG. 20. FIG. 21. FIG. 22. 
FIG. 23. FIG. 24. FIG. 25. Fic. 26, 
the form of a horseshoe. Meanwhile the nuclear 
membrane breaks down, so that the hyaline substance 
of the nucleus becomes continuous with that of the 
cell body surrounding it. A fresh phenomenon now 
becomes visible. A spindle-shaped arrangement makes 
its appearance consisting of a number of minute fibrils 
which connect together two points—the poles of the 
spindle — situated at opposite ends of the cell. The 
