RESULTS OF HYBRIDISATION 383 



may in part depend .on the struggles and interactions of these 

 in the course of development ; for, as we have often said, it does 

 not follow that everything represented in the inheritance finds 

 expression in development. Finally, it must be remembered 

 that the process of development implies interaction between 

 the inheritance and an appropriate environment, and that since 

 this appropriate environment is variable (within limits of the 

 embryo's viability) the result may again be modified by minor 

 peculiarities of nurture. It is, therefore, plain that prediction 

 as to individual results of crossing is out of the question. 



The Mendelian theory has thrown light on the variability 

 which has often been remarked when crosses have been effected. 

 Cross-breds are produced and inbred, and new forms appear in 

 their progeny. The Mendelians contend, in Mr. Bateson's 

 words, that " in all the cases which have been properly examined 

 these new forms are created by simple re-combination of characters 

 brought in by the original parents." 



SUMMARY. There are several well-known results of hybridisa- 

 tion : 



1. The hybrids may be an intermediate blend of the parental 



characters, as in mulattos, finch and canary, carrion 

 crow and hooded crow, and in many plants. 



A x B yields 



2. The hybrids may show a particulate juxtaposition with- 



out a blend of the parental characters, as in piebald 

 animals, or in the cross between male Lady Amherst 

 pheasant and female golden pheasant, 



A x B yields A + I 



3. The hybrids may resemble an ancestral form, whose 

 characters have not been recently patent, as in many 

 crossings of pigeons, red-eyed albino house-mouse and 



