2 INHERITANCE IN POULTRY. 



recently the law has been commonly accepted which is thus expressed by 

 Darwin (1876, Chapter XV) : "When two breeds are crossed their char- 

 acters usually become intimately fused together." Many cases of non- 

 fusing inheritance are now known and it is important to ascertain the rela- 

 tive frequency of the different kinds of inheritance and their relation to one 

 another. 



IvUcas (1850, p. 194) recognizes three methods of inheritance, which he 

 calls respectively that of election, of mixture, and of combination. They 

 are thus defined : Election results in imprinting on some or all parts of the 

 organism the characteristics of the father exclusively or those of the mother. 

 Mixture results in a mixed or simultaneous representation of the father and 

 of the mother on some or all of the parts of the organism. Its extreme is 

 fusion of characteristics. Combination results in the substitution of a new 

 characteristic in the place of any representative in a part or over the whole 

 of the organism. This new characteristic results from the interaction of 

 the two antagonistic ones just as a chemical combination often differs wholly 

 from the elements which have been united in its manufacture. 



Darwin (1876, Chapter XV) seems to recognize only two classes of inherit- 

 ance, viz., one in which characteristics blend and one in which they refuse 

 to blend. Of the latter class, however, there are two cases ; either the 

 hybrid receives all its characters from one of its parents only, or the hybrid 

 receives part of its characters from one parent, the rest from the other. 



Nageli (1884; 1898, p. 17) describes the different forms of inheritance 

 very clearly, thus : 



In the idioplasm of a germ cell arising from the crossing of unlike individuals the 

 micellar rows of the individual Anlagen have sometimes an intermediate constitution 

 and produce characteristics in the organism -which are intermediate between the char- 

 acteristics of the parents. Sometimes the micellar rows derived from the father and the 

 mother respectively lie side by side interchanged in the idioplasm of the offspring in 

 distinct groupings and may reproduce in the organism their respective characteristics 

 side by side, or only one of them may develop, while the other remains latent. (Clark's 

 translation.) 



Galton (1889, pp. 7, 12, 14) distinguishes three kinds of inheritance, as 

 follows : (i) particulate, or inheritance "bit by bit, this element from one 

 progenitor, that from another ; " (2) blending, as in human skin color ; this 

 may ' ' be none the less ' particulate ' in its origin, but the result may be 

 regarded as a fine mosaic too minute for its elements to be distinguished in 

 a general view;" and (3) exclusive, as in human eye color; although 

 ' ' there are probably no heritages that perfectly blend or that absolutely 

 exclude one another, but all heritages have a tendency in one or the other 

 direction, and the tendency is often a very strong one." 



The different types of inheritance are thought by various authors to be 

 characteristic of particular sorts of crossing. Isidore Geoffroy St.-Hilaire 

 insisted ' ' that the transmission of characters without fusion occurs very 



