i62 MENDELISM chap. 



showing a series of intermediate stages between two 

 characters has sometimes been brought forward in 

 opposition to the view that the characters of 

 organisms depend upon specific factors which are 

 transmitted according to tlie Mendelian rule. But, 

 as this case from poultry shows clearly, neither 

 the existence of such a continuous series of inter- 

 mediates, nor the fact that some of them may breed 

 true to the intermediate condition, is incompatible 

 with the Mendelian principle of segregation. 



In connection with intermediates a more cogent 

 objection to the Mendelian view is the case of the 

 first cross between two definite varieties thence- 

 forward breeding true. The case that will naturally 

 occur to the reader is that of the mulatto, which 

 results from the cross between the negro and the 

 white. According to general opinion, these mulattos, 

 of intermediate pigmentation, continue to produce 

 mulattos ; but when enquiry is pushed to discover 

 the basis upon which general opinion rests, it is 

 found to be nearly always uncritical and vague. 

 Quite recently an attempt to obtain more exact 

 information has been made by Davenport in the 

 United States. From the study of a number of 

 families he came to the conclusion that definite 

 Mendelian segregation occurs. According to him the 

 results can be expressed in terms of two factors, A 

 and By either of which, when present, produces the 

 characteristic pigmentation of the skin. Together 

 the two factors produce a darker effect than when 

 only one of them is present. Also, as in the silky 

 fowl, the effect produced by a factor is more marked 

 in the homozygous than in the heterozygous state. 



