2 54 BIOLOGY AXD ITS MAKERS 



was sho^^n lo 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 at all. This 

 led to the recognition of protoplasm as made up of a densely 

 staining portion called chromatin, and a faintly staining por- 



,r«^ 



■^N- 



t 



' ■ ... .^V :.>^ 4g 



_.- -< _,- . 



(if* 



Fig. 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 



