HEREDITY 



The equal share of egg and sperm in deter- 

 mining the character of offspring is well shown 

 in the following experiment. An albino guinea- 

 pig is one which lacks in large measure the 

 ability to form black pigment. Apparently it 

 does not possess some ingredient or agency 

 necessary for the production of pigment. Now, 

 if an albino male guinea-pig, such as is shown 

 in Fig. 15, be mated with a black female guinea- 

 pig of pure race, such as is shown in Fig. 14, 

 young are produced all of which are black, like 

 the mother, none being albinos, like the father. 

 Fig. 16 shows black offspring produced in this 

 way. Exactly the same result is obtained from 

 the reverse cross, that is, from mating an al- 

 bino mother with a black sire. It makes no 

 difference, then, whether the black parent be 

 mother or father, its blackness regularly domi- 

 nates over the whiteness of the albino parent, 

 so that only black offspring result. This fact, 

 which has been repeatedly confirmed, shows that 

 the black character is transmitted as readily 

 through the agency of the minute sperm-cell 

 as through the enormously greater egg-cell. 



Let us now consider what happens when egg 

 10 



