I02 GENERAL ORNITHOLOGY part ii 



more or less susceptible of modification by such means, they become 

 unlike their ancestors in various ways and to different degrees. On 

 a large scale is thus accomplished, by natural selection and other 

 natural agencies, just what man does in a small way in producing 

 and maintaining different breeds of domestic animals. Obviously, 

 amidst such ceaselessly shifting scenes, degrees of likeness or unlike- 

 ness of physical structure indicate with the greatest exactitude the 

 nearness or remoteness of organisms in kinship. Morphological 

 characters derived from examination of structure are therefore the 

 surest guides we can have to the blood-relationships we desire to 

 establish ; and such relationships are the natural affinities which 

 all classification aims to discover and formulate. As already said, 

 taxonomy consists in tracing pedigrees, and constructing the j^Aj/tem; 

 it is like tracing any leaf or twig of a tree to its branchlet, this to 

 its bough, this again to its trunk or main stem. The student will 

 readily perceive, from what has been said, the impossibility of 

 naturally arranging any considerable number of birds in any linear 

 series of groups, one after the other. To do so means nothing more 

 or less than the mechanical necessity of book-making, where groups 

 have to succeed one another, in writing page after page. Some 

 groups will follow naturally ; others will not ; no connected chain 

 is possible, because no such single continuous series exists in nature. 

 In cataloguing, or otherwise arranging a series of birds for descrip-- 

 tion, we simply begin with the highest — or lowest, if we prefer — 

 groups, and make our juxtapositions as well as we can, in order to 

 have the fewest breaks in the series. 



Morphology being the safest, indeed the only safe, clue to 

 natural affinities, and the key to all rational classification, the 

 student cannot too carefully consider what is meant by this term, 

 or too sedulously guard against misinterpreting morphological char- 

 acters, and so turning the key the wrong way. The chief difficulty 

 he will encounter comes from 'physiological adaptations of structure ; 

 and this is something that must be thoroughly understood. The 

 expression means that birds, or any animals, widely different in the 

 sum of their morphological characters, may have certain parts of 

 their organisation modified in the same way, thus bringing about a 

 seemingly close resemblance between organisms really little related 

 to each other. For example : a phalarope, a coot, and a grebe, all 

 have lobate feet ; that is, their feet are fitted for swimming purposes 

 in the same way, namely, by development of flaps or lobes on the 

 toes. A striking but very superficial and therefore unimportant 

 resemblance in a certain particular exists between these birds, on 

 the strength of which they used to be classed together in a group 

 called Pinnatipedes, or "fin-footed" birds. But, on sufficient ex- 

 amination, these three birds are found to be very unlike in' other 



