io6 GENERAL ORNITHOLOGY part ii 



bird having such palatal characters would also be found to possess 

 such imperfect wing-apparatus. But this would be going too far : 

 in fact, we know that the tinamous {Dromceognaih(c) have such a 

 palate, yet have a keeled sternum and functionally developed wings. 

 The real use and proper application of such generalisations is to 

 teach the lesson, that creatures exhibiting such modified combina- 

 tions of characters are genetically related to each other just in the 

 degree to which they possess characters in common, and are 

 genetically remote from each other in the degree to which they do 

 not possess characters in common : i.e. that their similarities and 

 distinctions of structure are sure indexes of their natural affinities. 

 To take another case, derived from consideration of a large number 

 of existing birds : it is an observed fact, that a particular arrange- 

 ment of the plates upon the back of the tarsus, a peculiar modifica- 

 tion of the lower larynx or voice organ, and an undeveloped or 

 abortive condition of the first large feather on the hand, are found 

 associated in a vast series of birds, constituting the group of Passeres 

 called Oscines. What possil^le connection there can be between 

 these three separate and apparently independent modifications we 

 cannot even surmise ; but that they have some natural and necessary 

 connection we cannot doubt, and that the connection is causal, not 

 fortuitous, is a logical inference from the observed fact, that birds 

 which present this particular combination are also closely related in 

 other structural characters ; that is, that they have all been 

 subjected to operative influences which have conspired to produce 

 the modifications observed. Given, then, a bird, with a known 

 oscine larynx, but unknown as to its feet and Avings, it Avould be 

 a reasonable inference that these members, when discovered, would 

 present the characters observed to occur in like cases. But the first 

 lark {Alauclidce) examined would show the inference to be fallible ; 

 for the tarsus of such a bird is diff"erently disposed, though a lark 

 has an elaborate singing apparatus, and only nine instead of ten 

 developed primaries. Once more : the development of a keeled 

 sternum, a peculiar saddle-shape of certain vertebrae, and lack of 

 true teeth, are characters coexisting in all the higher birds ; and, 

 as far as these birds are concerned, we have no hint that such a 

 combination is ever broken. In fact, however, the singular Creta- 

 ceous Icldhyornis shows us a pattern of bird in which a well-keeled 

 sternum and perfectly formed wings coexist with teeth in reptile- 

 like jaws and with fish-like biconcave vertebrae. What Ave learn 

 from this case indeed breaks down one of the most precise defini- 

 tions we might have made (and indeed did make) respecting birds 

 at large ; but in its failure Ave are taught hoAv great is the modifica- 

 tion of geologically recent birds from their primitive generalised 

 ancestry ; Ave learn something likeAvise of the steps of such 



