104 GENERAL ORNITHOLOGY part n 



dipper (family Cinclidce) and a loon (family Colymbidm) are analogous, 

 in so far as both are fitted to pursue their prey by flying under 

 water ; but they stand near opposite extremes of the ornithological 

 system ; they have little affinity beyond their common birdhood — 

 very diiferent structure being modified' to attain the same end. So 

 again, conversely, the crow has vocal organs almost identical in 

 structure with those of the nightingale, and the organisation of the 

 two birds is in other respects very similar; their affinity or 

 homology is therefore close, though the crow is a hoarse croaker, the 

 nightingale an impassioned musician. 



The Reason why Morpholog'ieal Classifleation is so important 

 as to justify or even require its adoption has been very clearly 

 stated by Huxley, whose words I cannot do better than quote 

 in this connection. Speaking of animals, not as physiological 

 apparatuses merely ; not as related to other forms of life and to 

 climatal conditions ; not as successive tenants of the earth ; but as 

 fabrics, each of which is built upon a certain plan, he continues : 

 " It is possible and conceivable that every animal should have been 

 constructed upon a plan of its own, having no resemblance whatever 

 to the plan of any other animal. For any reason we can discover 

 to the contrary, that combination of natural forces which we term 

 Life might have resulted from, or been manifested by, a series of 

 infinitely diverse structures ; nor would anything in the nature of 

 the case lead us to suspect a community of organisation between 

 animals so different in habit and in appearance as a porpoise and a 

 gazelle, an eagle and a crocodile, or a butterfly and a lobster. Had 

 animals been thus independently organised, each working out its 

 life by a mechanism peculiar to itself, such a classification as that 

 now under contemplation would be obviously impossible ; a morpho- 

 logical or structural classification plainly implying morphological or 

 structural resemblances in the things classified. 



" As a matter of fact, however, no such mutual independence of 

 animal forms exists in nature. On the contrary, the members of the 

 animal kingdom, from the highest to the lowest, are marvellously 

 connected. Every animal has something in common with all its 

 fellows ; much, with many of them ; more, with a few ; and usually, 

 so much with several, that it difi'ers but little from them. 



"Now, a morphological classification is a statement of these 

 gradations of likeness which are observable in animal structures, and 

 its objects and uses are manifold. In the first place, it strives to 

 throw our knowledge of the facts which underlie, and are the cause 

 of, the similarities discerned,- into the fewest possible general 

 propositions, subordinated to one another, according to their 

 reater or less degree of generality ; and in this way it answers the 

 purpose of a memoria fechnica, without which the mind would he 



