THE FEEDING OF NESTLING BIRDS 205 



for such species to carry food in the mandibles. And in such 

 a proper restriction of the term "regurgitation" as I have made 

 in this paper, and as I believe the majority of ornithologists have 

 been accustomed to use the term, it seems to me very improbable 

 that birds which practice regurgitation would alternate with 

 solid food. Food apparent in the bill may not disprove that 

 the mouth is full likewise, and that the surfeit may extend 

 well into the gullet; but that the removal of this surfeit from 

 the throat or gullet is to be interpreted as regurgitation is quite 

 beyond the limits of good terminology. I believe, therefore, 

 that food visible in the bill is very good evidence against 

 regurgitation. 



One other point to be taken into account is the presence or 

 absence of action of the pharyngeal muscles. While this may 

 often be a little obscure and uncertain, especially for inexperienced 

 observers, it nevertheless may be regarded as important circum- 

 stantial evidence. If muscular activity is clearly present a 

 presumption is established in favor of regurgitation; but if no 

 muscular activity can be determined such a presumption cannot 

 be claimed, to say the least. 



In conclusion I may be permitted to suggest that we may, 

 in the future, find that there is greater significance in the 

 comparative study of the manner in which nestlings are fed 

 than has hitherto been recognized. Among the lower orders 

 of birds we find a method of feeding the young which we will 

 have little difficulty in regarding as primitive. In the higher 

 birds, such as the Passeres, we find developed a distinctly com- 

 plex performance. Between the primitive and complex pro- 

 cesses alluded to, we find feeding methods which may be regarded 

 as transition stages. Without, at this time, attempting a too 

 rigid arrangement of these feeding processes, as to their natural 

 and phylogenetic sequence, we may at least be justified in the 

 conclusion that the problem deserves much further study. 

 Whether any importance might be attached to such a quasi- 

 physiological process in the determination of affinities it would 

 be premature to speculate. But that this may be no more 

 than a random suggestion, only future investigation can 

 determine. 



