148 



ORTHOGENETIC EVOLUTION IN PIGEONS. 



to the dividing-line that is often seen in young pigeons; but in adults this fold is 

 usually smoothed out, either by the feathers of the two sides coming together or 



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TEXT-FIOORE 29. 



A. Adult male, African owl. x 1. Wilson del., March 1900. In this owl-pigeon the frill is more highly developed 



than in the homers shown in text-fig. 27. Some feathers of the left side of the upper breast turn strongly towards 

 the right side. Just above this misdirected mass of feathers are two imperfect rows of feathers which curve out- 

 wurd to right and left away from the median line. These variant feathers arise from the median tract and 

 develop later than the lateral feathers. 



B. Adult hybrid, Zenaidura x Streptopelia risoria. X 1. Wilson del., March 1900. Usually there is a well-marked 



crease running through whole breast. At times one or more feathers at different points are tilted up edgewise. 



C. The same. The profile view shows the condition seen at one time. 



by new feathers coming in, so as to make the tracts coalesce and form one even 

 surface. This pigeon has sometimes only 2 or 3 feathers twisted or turned out at 

 the middle height of the breast; above this point the median seam or fold extends 

 well up the neck, much as it does in young birds in first plumage. Sometimes more 

 feathers 3 to 5 are turned out into the frill. Apparently there is some slight con- 



