No. 4.] HEREDITY AND THE DAIRY COW. 11 



crossed with the whites. One-third of the whites will breed 

 true to white, while the other two-thirds bred together will 

 produce three whites to one red, exactly as did the first gener- 

 ation of hybrids. 



This all shows clearly why the successive oflPspring of the 

 same parents vary so much in character. The parents are 

 producing a great variety of gametes, and the law of chance 

 alone regulates the way in which they come together. If we 

 consider the fact that gametes possess a large number of 

 factors, and all of them are subject to the law we have been 

 considering, we see at once that we will have an almost in- 

 finite number of kinds of individuals. For instance, suppose 

 we add the factor for horns to the white-faced Hereford, and 

 the factor for lack of horns (polled) to the red-faced Dur- 

 hams. The gametes for the Hereford would be represented 

 by 11 W and for the Durhams by P R. When brought to- 

 gether the resultant individual would be P II W R. When 

 these cells divide to form gametes, the red of the Durhams 

 will not be found in the same gamete with the white of the 

 Hereford, but since red has no antipathy for a polled head 

 or for one with horns, it may be found with either P or H, 

 but not with both, because polled and horned cannot go to- 

 gether. The gametes will therefore have the constitution of 

 P W or P R, and H W or II R. Now these are all produced 

 in equal numbers, and so we may have animals produced 

 composed of all the possible combinations of these four kinds 

 of gametes. We may have P W P R, P W H W, P W II R, 

 P R H R, H W H R, P W P W, P R P R, II W H W^ 

 or H R H R. 



When we consider that animals possess a great many 

 charactei-fe presumably all represented by factors in the 

 gametes, we realize the great number of possible combina- 

 tions and consequently the great number of different gametes 

 that will be formed. This explains, then, the fact so uni- 

 versally observed, that even successive offspring of the same 

 parent differ greatly in their constitutional make-up. 



I will not attempt to carry any farther at this time the 



