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of animals stands on another and different footing; results of eco- 

 nomic importance have not been achieved so far, and it is still 

 doubtful, theoretically, whether the new methods are applicable ta 

 the problems in which practical men are interested. Stockbreeders, 

 as a rule, have not, up to the present, devoted much attention to 

 the matter, and it would seem that the mathematical aspect, which 

 finds a place even in professedly popular accounts of the theory, 

 is an obstacle which, to some minds, proves insurmountable. If, 

 however, the facts established by the Mendelian school, be disso- 

 ciated from the theories which have been framed to explain them,, 

 there is nothing in the new science that the ordinary reader need 

 have any difficulty in comprehending. 



In the first place, to clear the path, it is necessary to point out 

 that Mendelian methods and discoveries are concerned with, and 

 confined to, the inheritance of distinct and mutually exclusive cha- 

 racters only. For example, a flower is either coloured or white;, 

 colour and whiteness are an example of such characters. Thus 

 the Mendelian can predict what will happen when, say, a white 

 breed of rabbit is mated with a coloured one; he cannot predict 

 the result of mating a large animal with a small one ; he can fore- 

 tell the colour of the eyes of the children of two blue-eyed pa- 

 rents ; he is ignorant of the law determining their height. Confining 

 our attention, then to the inheritance of sharply defined characters,, 

 of which colour will serve as a type, the root principle of Mendelism 

 may be simply stated. It is that many, if not all, such characters 

 behave as distinct units in inheritance, and may be present (or 

 absent) in the off-spring, dissociated from the other characters present 

 in either of the parents, in accordance with certain definite numerical 

 laws. For example, a child may have the blue eyes of its father but 

 all its other colour characters from its brown-eyed mother, moreover, 

 the Mendelian law enables us to affirm that the blue-eyed child 

 has no dark eyed character in its " blood," even though its mother 

 had dark eyes ; in other words, the offspring of this blue-eyed child y 

 if mated with another blue-eyed individual, will never show any 

 " reversion " to dark eyes. It cannot, however, be asserted that 

 the offspring of two dark-eyed parents will all have dark eyes, for 

 it is a fact that, whereas the blue eye is always " pure, " in the 

 sense that it breeds true, the dark eye, on the other hand, is so- 

 metimes pure and sometimes impure, the " impurity " consisting in 

 the fact that the blue-eyed character is sometimes latent and likely 

 to appear in the offspring. In Mendelian terminology, dark eye is 



