28 THE EVOLUTION OF LIVING BEINGS. 



HYBRIDS : to designate all individuals able to produce more 

 than one kind of gametes, e. g. gametes of different 

 constitutions, (in some cases all of these or part of these 

 are non-viable}. Hybrids consequently are poly gametic. 

 In many cases the hybrid nature of an individual 

 can be demonstrated by careful breeding alone, e. g. 

 in those cases in which the uncontaminated progeny 

 is visibly heterogeneous; in many other cases f. i. 

 in all cases of albinism, hybrid analysis is required in 

 addition. 



MODIFICATION : to designate the non-transmittdble effect of 

 external circumstances. 



