546 Mr. R. Shelford on some 



rectrices. The two upwardly-diverging tracts noticed in 

 Stage 4 are present here also ; in the adult they join the 

 pt. femoralis. 



PL humeralis. — Dorsally it is continuous with the pt. 

 alaris and pt. spinalis; in the adult it runs over on to the 

 ventral surface to fuse with the pt. ventralis ; but at present 

 this connection is not yet set up. 



Pt. ventralis is in two halves, perfectly separate from each 

 other ; the pt. colli, forking just before its termination, runs 

 into each half. A great increase in the length of the two 

 ventral branches may be noted Avhen this stage is compared 

 with Stage 4. At the level of the knee (with the leg drawn 

 up) each branch of the ventral tract sends upward and 

 outward towards the proximal end of the humerus a sparse 

 and narrow tract, the commencement of which was just 

 indicated in Stage 4. In the adult these two narrow tracts 

 sweep round over the point of the shoulder to join the pt. 

 hufneralis and pt. ventralis at the point of fusion of those two 

 tracts ; an oval island-like apterium is consequently left, 

 which apterium I propose to call the apterium pectorale ; 

 though not completely formed at Stage 5, I have in PI. X. 

 fig. 1 indicated its future outline by a line. 



Pt. alaris. — Save that the under coverts are no further 

 developed than in Stage 4, the wing has assumed the adult 

 appearance, and the birds must be quite capable of flying for 

 short distances. 



The other pterylse call for no special notice. 



General Summary. 



The nestlings of the Bucerotidae here examined are so 

 liio-hly specialized, no doubt as a result of the extraordinary 

 habits of nidification, that a study of their external characters 

 has not proved of any taxonomic value, though possibly the 

 nestlings of the Upupidse and Irrisoridse might exhibit 

 characters which would help to bridge over the gap between 

 these families and their allies, the Hornbills, 



The large dorsal apterium of the Upupidse is in the adult 

 Hornbill represented only by a minute apterium between the 



