EVOLUTION AND ANIMAL LIFE 



suggestive classification of these inheritance categories as 

 follows : 



In cross mat ings and by " cross mating," students of hered- 

 ity do not necessarily mean mating between distinct species or 

 even varieties, but mating between parents which disagree in 

 the condition of one or more specifically referred to characteris- 

 tics in cross mating between the parents A and B, if we con- 

 sider a single pair of corresponding characters a and b which 

 differ in the two parents, the young produced by the crossing 

 may (1) all present the same parental character a without any 

 trace of the character b, the character a being then termed 

 dominant or prepotent or prevalent, the other recessive or 

 latent; or, (2) the young may all agree in presenting a new char- 

 acter differing from the parental characters a and 6, this new 

 character apparently being a simple physical mixture or a real 

 chemical combination or blending of a and b ; or (3) , the young 

 may differ from one another in regard to the parental characters 

 a and b, some showing the character a, some showing the char- 

 acter b or (4) the young may differ among themselves in regard 

 to the characters a and 6, some showing the character a, some 

 the character 6, and some various characters intermediate be- 

 tween a and fr; or (5) the young may show the characters a and 

 b side by side in each individual in small separated parts, even 

 in neighboring but distinct cells. These differences undoubt- 

 edly depend partly on the nature of the characteristics them- 

 selves, partly on the kind of organism, and partly on extrinsic 

 influences. It is obvious also that for certain characteristics by 

 no means all five of these ways are open. Many characters are 

 so wholly antagonistic that no blend nor any mosaic of them can 

 occur in a single individual, leaving only ways (1) and (3), viz., 

 exclusive or alternative inheritance open to them. 



To these five general categories of the actual transmission 

 of certain obvious parental characters may here be added for 

 consideration those cases of the appearance in the young of a 

 character or characters having no obvious relation to either a 

 or 6, but sometimes explicable as reversions or reappearances 

 of characters possessed by ancestors more or less remote and 

 other times as obviously wholly new and heretofore never ex- 

 istent characters which, if pronounced, are called "sports" or 

 sudden or discontinuous variations. Also must be taken into 

 account the possible appearance among the young, of a few to 



