42 THE GENETIC AND THE OPEBATIVE EVIDENCE 



started as females (ZW), which is inconsistent with the dislocation 

 hypothesis. The alternate would be that in all these cases the Z part 

 always included the region of the oviduct, which seems improbable. 



There is another possibiUty, viz, that in birds a sex-factor is carried 

 by the W chromosome, and ZW is a female not because of one Z, but 

 due to the presence of W. If so, then one Z or two Z's might give the 

 same result, viz, female. If a bird started as female, (ZW) and chromo- 

 somal dislocation occurred, then the Z parts would be female and the 

 male part W. Until we get evidence on this point it is not worth 

 elaborating. Without genetic evidence from hybrids, the interpretation 

 of hermaphrodites in birds can have at present only a speculative 

 interest. We may hope some day to get the same kind of evidence 

 as in the case of Drosophila. Hermophrodite hybrid pheasants that 

 have been often described might seem to furnish a hopeful field, for 

 they appear to be quite common and to show characteristics of both 

 races. As yet, however, no one has, I think, succeeded in finding a 

 simple interpretation of the results. It is also not unlikely that many 

 of the pheasant cases are not true hermaphrodites, but due to failure 

 of normal development of the reproductive gland, which gives an 

 intermediate or mixed type of secondary sexual characters. 



