18/3.] M R. O. SALVIN ON THE TAIL-FEATHERS OF MOMOTUS. 431 



been removed from the left-hand feather. Figure 3 (p. 432) shows the 

 process of denudation still further advanced. In all these three birds 

 it will be noticed that the feathers in question have grown symme- 

 trically, both being of nearly equal length. Figure 4 (p. 432) repre- 

 sents the tail of a Prionirhynchus platyrhynchus, where these feathers 

 have not grown symmetrically, but the left-hand one has been de- 

 veloped sooner than the right-hand one. What has happened? 

 The bird expecting to find two feathers upon which to operate has 

 commenced to nibble not only the left central rectrix but also the 

 next rectrix on the right-hand side! But it seems to have not felt 

 very certain about the state of its tail, for it has wandered off to one 

 of the others and commenced nibbling it also. When, however, the 

 proper right-hand feather appeared these mistakes have been dis- 

 covered and the work recommenced in the usual way. I can inter- 

 pret in no other way the state in which the feathers on the right- 

 hand side of the tail of this bird appear. 



Fig.]. 



Tail of M. ?e$soni,jr. ; two central Tail of M. mexicanus; the central rec- 

 rectrices shaded. trices, not fully grown, are shaded. 



It will be seen that the growing feathers before they are stripped 

 have naturally narrower webs at the place where they are subse- 

 quently denuded. This perhaps arises from the constant attrition 

 of the webs in the growing feathers weakening their development ; 

 and if so, we see that by constant perseverance on the part of the 

 birds in stripping this portion of their tail-feathers, a permanently 

 bare place in the rachis might ultimately be produced, and that at 

 last, in the course of many generations, feathers would grow with 



