THE ORIGIN OF GYNANDROMORPHS. 105 



species of birds the male plumage is not affected by ovarian secretions, 

 as it is in poultry and in ducks, but is due directly to genetic factors 

 that act effectively in the male but not in the female. It ought to 

 be comparatively easy to find this out for each race by means of 

 gonodectomy. 



The other possible explanation is that although in a bird genetically 

 male (ZZ) on one side and female (Z) on the other, the secondary 

 sexual characters would be female; yet if the ovary should become 

 diseased or old and its secretions diminished, a point might be reached 

 where the secretion could no longer hold in check the full develop- 

 ment of the male part. The bilateral gynandromorph in birds would 

 on this view represent only a transient stage. In point of fact, none 

 of them have been kept alive for any length of time, so that we do 

 not know that they would hold their superficial peculiarity. An 

 alternative to this view that the secretions were insufficient because 

 of disease or age is to suppose that the ovary is abnormally small 

 from accident or heredity. In this case the gynandromorph stage 

 would be more permanent. Such birds would be expected in all cases 

 to have an ovary, or at least to have some traces of one, unless the 

 species resembled Mallards or Sebrights, where the testis influences the 

 plumage. 



The results that Riddle has reported concerning intersexes in hybrid 

 pigeons do not call for detailed review here, since the phenomena 

 recorded relate largely to behavior. Riddle believes that under 

 " conditions of overwork" a female produces eggs, some of which are 

 male-producing, others female-producing, as shown by mating such 

 females to the males of their own species when equal numbers of 

 males and females are produced. But such overworked eggs, if fertil- 

 ized by a male of a different genus, produce predominantly female birds. 

 The result, however, is not attributed to the male, or to the cross, but 

 to some change in the egg that causes a reversal of the sex tendency. 



The only case that Riddle has reported in which the color inheritance 

 is given, so that one can follow the sex-linked heredity in connection 

 with the abnormal sex ratio, is that recorded in the Naturalist for 

 1916. 1 The first 17 doves were 5 male to 12 female doves; the second 

 17 doves were 4 males to 13 females; the last 17 doves were 2 males to 

 15 females. The cross was made between Streptopelia alba male 

 and St. risoria female. As R. M. Strong had previously shown, the 

 expectation here is for dark sons and white daughters. Since the 

 reciprocal cross gives all dark offspring, the factor involved is sex- 

 linked and not merely sex-limited. Riddle obtained only dark males 

 and white females, except two that were dark (one being questioned 

 by himself). Strong also found a few dark exceptions, as did also 

 Staples Brown. As Bridges has shown, these exceptions can be 



1 Reproduced and expanded in the Journal of the Washington Academy of Sciences, June 1917. 



