LECTURE V 

 HEREDITY 



IN this lecture we have to consider the factors at work 

 which determine the degree of similarity between parent 

 and offspring, or between the various offspring of the same 

 parents. The problem is fundamentally the same through- 

 out the whole animal and vegetable kingdoms, though 

 simplified in degree in the case of the lowest, unicellular, 

 organisms. In what follows we shall neglect these and 

 confine ourselves to the higher organisms, where the 

 problem is conditioned by two main factors. 



Firstly, that the bridge between two generations is the 

 minute germ-cell or gamete which, being unicellular, is of 

 a different order of structure from either the parent from 

 whom it was derived, or the individual into which it 

 develops. 



Secondly, that each individual of the new generation 

 is usually produced by the fusion of two cells (gametes) 

 derived from different individuals of the parent generation. 



The fact that the bridge between parent and offspring 

 is the minute unicellular gamete at once raises the question 

 of what is the physical substratum on which heredity 

 depends. Is there any part of the gamete which can be 

 recognised as presenting those properties which we 

 should expect this substratum to possess ? 



