12 



INHERITANCE, FERTILITY, AND SEX IN PIGEONS. 



risoria. The arrangement of this part of the formula indicates that the female 

 (used as dam in this cross) had a pure humilis father and a mother which was 

 hybrid between IniiniUs and risoria. The hyphen (-) is used instead of a small 

 symbol (x) to indicate the more remote unions or matings. The hybrid that results 

 from the cross of the two birds of cross No. 23 just cited will itself be desig- 

 nated by the formula exactly as written above, i.e., turtur-orientalis X humilis x 

 hwniKs-risona. 



In all of the tabulated breeding records of the succeeding chapters the composi- 

 tion formula for the male bird which is used as sire is written as the numerator 

 and that of the female as the denominator of a fraction. It is believed that as the 

 reader proceeds he will find the method followed here is an easy and natural one and 

 that it gives completely and in reasonably compact form the pedigree of the bird. 



Included in the preceding list of primary crosses are the data for the number of 

 males and of females produced by each cross. A general statement concerning the 

 fertility of the hybrids is also given for most of the crosses. In addition, it has 

 been thought well to give the degree of relationship of the two forms crossed, i.e., 

 whether they are of specific, generic, subfamily, or family distinction. In some of 

 these cases the degree of distinction has been more fully indicated by plus ( + ) 

 and minus ( ) signs placed after the words "species," "genera," etc. The desig- 

 nation "gen. + " then is intended to state that the two forms of a particular cross 

 belong to different genera and that these two genera are perhaps more unlike than 

 are those genera designated "gen. -." 



Table references to 72 primary crosses. 



Not tabulated. 



- Data not available. 



The list of crosses containing the summaries and statements just mentioned 

 gives, in a, very condensed form, clear and adequate evidence for two important 

 conclusions which are treated at length in succeeding chapters. These conclusions 

 :in- ( 1) that the hybrids which arise from crosses of forms more and more distantly 

 related show less and less fertility, and (2) that the sex of the hybrids which arise 

 troin crosses of forms more and more distantly related becomes more and more 

 predominantly male. 



