400 External Changes in Birds, 



the species, by which every typical standard may be easily 

 traced to its ultimate ramifications ; some of the most valuable 

 of these characters, in the feathered race, being afforded by 

 peculiarities in the mode of moulting. To illustrate this, I 

 may cursorily adduce the various finch-like Sturnidse ( Aglaius, 

 M61othrus, Dolichonyx, &c); extreme modifications of the 

 Corvus type ; as are also, however unlike they unquestionably 

 appear, the genera v41auda, and even Ammodramus. All 

 these, I have ascertained either from direct observation, or 

 from competent sources, shed the nestling primaries the first 

 season, which is not the case with any modification of the 

 fringillidous type, or of the dentirostral. If other characters 

 be wanting, which point alike to the same conclusion, I may 

 mention the constant presence of a craw, or enlargement of 

 the oesophagus, in all the jPringillidae, and its invariable ab- 

 sence in all, even the most aberrant, modifications of the 

 Corvus type ; all the latter, too, preserve the ambulatory 

 mode of progression, which, in perfection, is not observable 

 in any ifyingillidae, not even Plectrophanes. Again, other 

 characters of distinction between these two equivalent divi- 

 sions are sufficiently visible in the general aspect of the bill, 

 even where the extremes approximate : all the jPringillidae, 

 for instance (to which I would restrict the appellation Coni- 

 rostres), possess what may be strictly defined a bruising, or 

 compressing, instrument ; whereas the general character of the 

 same organ in the other division is rather what may be aptly 

 termed a thrusting one, intermediate in its structure between 

 those of the i^ringillidae and Dentirostres ; in which last group 

 the bill is modified into either a snapping, holding, or tugging 

 instrument, as the case may be : sometimes all three, as in 

 Fireo. 



However, to return to the proposition I was just advancing, 

 that, physiologically speaking, there are no combinations of 

 distinct types, no intermediate organisms, save those between 

 a central type and its ultimate ramifications : the general 

 structure may be intermediate, and, consequently, the situation 

 a species holds in the adaptive system, the office which it may 

 have to perform in the general economy of the universe ; but 

 the latter does not constitute affinity ; neither, strictly speaking, 

 is it analogy ; therefore I must distinguish it by another term, 

 approximation. 



As I shall have occasion to make use of these words fre- 

 quently, as I proceed, it will be necessary, before advancing 

 further, to define the precise meaning which I attach to them, 

 however much this may appear digressing from the subject 

 more immediately in hand. 



