266 CARL C. LINDEGREN 



In many types of organisms the chromosomes are always separated by the 

 nuclear membrane from the cytoplasm. The mitochondria (like the chromo- 

 somes) are relatively non-homogeneous, but apparently the balance of their 

 activities is not so critical since no specific devices appear to be required to 

 limit their reproduction or activity. The cytoplasm is probably heterogene- 

 ous also, with every separate eternal component having the same continuity 

 in time as the chromosomes. However, it comprises substances transmitted to 

 the daughter cells in a manner which is apparently subject to control by the 

 environment, and this may constitute the basis for differentiation. In the 

 germ line, the entire cytoplasmic potential must be maintained. In fact, the 

 main function of the germ line under this hypothesis would be to maintain 

 an intact cytoplasm. The integrity of the chromosomes is usually provided 

 for in either the somatic or the germinal tract. Defects in the extra chromo- 

 somal apparati are reconstituted in an outcross, thus differentiating so-called 

 cytoplasmic from genie inheritance. 



