The Making of Species 



It is a significant fact that under abnormal 

 conditions the feathers of birds tend to disappear 

 precisely on those spots where the pcecilomeres 

 of Bonhote occur. 



Thus in a sickly cage bird the feathers 

 frequently show a tendency to fall off on the 

 following spots : crown of head, lores, jaws, 

 head generally, rump, vent and thighs. 



Many wild birds as, for example, the cranes 

 display patches of naked skin on the head, 

 and these are usually situated on pcecilomeres. 

 Similarly, natural excessive developments of 

 plumage tend to occur on the pcecilomeres, or, 

 rather, the spots characterised by pcecilomeres 

 for example, the train of the peacock. Loral 

 plumage, it is true, is seldom long, but is often of 

 a peculiar nature. 



Colour mutations tend to occur on the pcecilo- 

 meres. Thus it is that these pcecilomeres often 

 form the distinctive characters and markings of 

 allied species. This is precisely what we should 

 expect if the pcecilomeres correspond to bio- 

 logical molecules and mutations are the result of 

 the rearrangement of the constituent parts of 

 these molecules. 



Still more significant is the fact that the colour- 

 markings in hybrids tend to follow pcecilomeres. 



Bonhote has performed a large number of 

 experiments in hybridising ducks. Some of his 

 hybrids were produced from three pure ancestors, 



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