254 BIOLOGY AND ITS MAKERS 
was shown to be of great importance in cell-life—to be a 
structure which takes the lead in cell division, and in general 
dominates the rest of the protoplasm. 
Chromosomes.—After dyes came into use for staining the 
protoplasm (1868), it became evident that certain parts of it 
stain deeply, while other parts stain faintly or not atall. This 
led to the recognition of protoplasm as made up of a densely 
staining portion called chromatin, and a faintly staining por- 
Fic. 77.—An Early Stage in the Development of the Egg of a Rock- 
Limpet. (After Conklin.) 
tion designated achromatin. ‘This means of making different 
parts of protoplasm visible under the microscope led to im- 
portant results, as when, in 1883, it was discovered that the 
nucleus contains a definite number of small (usually rod- 
shaped) bodies, which become evident during nuclear divi- 
sion, and play a wonderful part in that process. These bodies 
take the stain more deeply than other components of the 
nucleus, and are designated chromosomes. 
Attention having been directed to these little bodies, 
continued observations showed that, although they vary in 
