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 peecilomeres, or, 
rather, the spots characterised by pcoecilomeres— 
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 peecilo- 
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, 
292 
