4 2o THE POPULAR SCIENCE MONTHLY 



Fig. 2. An Albino female Guinea-fig. Its ovaries were removed and in their place 

 were introduced ovaries from a young black guinea-pig. Compare Fig. 1. 



transplanted from one individual into another retains the character 

 which it originally had, quite unaffected by the changed body with 

 which it is associated. This Dr. John C. Phillips and the writer have 

 recentty shown in the following way. The ovaries were removed from 

 a young black guinea-pig, Fig. 1, and these were transplanted into the 

 body of a white guinea-pig, previously castrated, Fig. 2. The white 

 guinea-pig was now mated with another white guinea-pig, Fig. 3. 

 Normal white guinea-pigs produce only white offspring when mated 

 with each other, but these two have now produced in three successive 

 litters six young, all black. Three of these are shown in Fig. 4. 

 Evidently the germ-plasm of the black guinea-pig retained its original 

 character even after transplantation into the body of a white one. 



In order better to understand the processes of heredity we should 

 be familiar with what takes place when a new individual is formed. 

 The new individual, whether an animal or a plant, has its beginning in 

 the union of two bits of germ-plasm, an egg cell furnished by the 

 mother and a sperm cell furnished by the father. Whether the union 

 of the germ-plasm takes place within the maternal body or not is quite 

 immaterial ; among a great many animals it does not. 



The new individual, it will be observed, is dual in origin, and to 

 its dying day it retains a dual nature. For the maternal and paternal 

 contributions of germ-plasm retain a certain distinctness as we shall 

 see, and may in part separate from each other at reproduction. 



Each germ-cell (egg or sperm), so far as its contribution to heredity 

 is concerned, stands for a complete organism of its species, bears the 

 potentialities of a complete organism, and under appropriate condi- 



