Phenomena of Inheritance 113 



Other forms of transmission are known in which substances 

 are carried over from one generation to the next through the egg, 

 but they are probably not cases of true inheritance. Among these 

 are the occasional transmission of immunity through the mother 

 but never through the father, the carrying over of particular 

 chemical substances such as fat dyes through the egg but not 

 through the sperm, and the transport of symbiotic or parasitic 

 organisms, such as algae, bacteria, etc., through the female sex 

 cell but not through the male cell. These substances or micro- 

 organisms are to be regarded as inclusions in the egg rather than 

 as any permanent part of the germinal organization; consequently 

 they are not inherited in the strict sense of that term. 



III. MENDELIAN INHERITANCE IN MAN 



The study of inheritance in man must always be less satisfac- 

 tory and the results less secure than in the case of lower animals 

 and for the following reasons: In the first place there are no 



FIG. 36. MULATTO HUSBAND AND WIFE AND THEIR SEVEN CHILDREN 

 ranging in color from the one on left who "passes for white" to the 

 youngest who is typically black. (From Davenport.) 



