236 SECRETS OF ANIMAL LIFE 



and so on. The doubt left in one's mind is whether 

 the auxiliary hypotheses which make difficult cases 

 conformable are triumphs of human ingenuity or 

 indices of the subtlety of life. When we are led 

 by other authorities to contemplate the disintegra- 

 tion or fractionization of the factors of certain unit 

 characters, our faith is strained by what seems so 

 like a contradiction in terms. But the scientific 

 position is to experiment and see. Very interesting 

 on another line are the experiments of T. H. Mor- 

 gan * and his collaborators on the fruit-fly Droso- 

 phila, showing that " every character is the realized 

 result of the reaction of hereditary factors with each 

 other and with their environment." Flies of a 

 race with a peculiar hereditary abnormality will 

 develop normally if raised in a dry environment, 

 but the presence within them of the factor for 

 abnormality may be demonstrated by rearing their 

 offspring in moisture. In other words, the ex- 

 pression of even Mendelian characters requires an 

 appropriate nurture. 



Professor Wilson lays stress on the fact that 

 theoretical difficulties need not hinder the breeder 

 from utilizing the Ariadne thread which Mendel has 

 put into his hand. For it is becoming increasingly 

 clear that Mendelism can enable a breeder or 

 cultivator to reach his desired result more surely, 

 more rapidly, and more economically. His new 

 knowledge shows him how desirable qualities of the 

 unit character type can be grafted on to a stock, 



1 The Mechanism of Mendelian Heredity. Constable, 1915. 



