32 CHAPTERS ON THE NATURAL HISTORY 



observation that, among the endless diversities of living things, 

 some constantly resemble one another so closely that it is im- 

 possible to draw any line of demarcation between them, while 

 they differ only in such characters as are associated with sex. 

 Such as (litis closely resemble one another constitute a morpho- 

 logical species; while different morphological species are defined 

 by constant characters which are not merely sexual. 



"The comparison of these lowest groups, or morphological 

 species, with one another, shows that more or fewer of them 

 possess some character or characters in common — some feature 

 in which they resemble one another and differ from all other 

 species — and the group or higher order thus formed is a genus. 

 The generic groups thus constituted are susceptible of being ar- 

 ranged in a similar manner into groups of successively higher or- 

 der, which are known as families, orders, classes, and the like." 

 And. added to this, it may lie said that, according to quite similar 

 principles, we create the intermediate groups in nature, or those 

 intended to contain the subspecies, the subgenus, the subfamily, 

 the suborder, the subclass, and also such others as the superfumUy 

 and the superorder, anil so on. 



So much for true or natural classification; but we have another 

 kind, differing from it. however, only in degree, and I refer to all 

 forms of artificial classification. The artificial classification of 

 living forms in nature depends upon the selection of easily ob- 

 served features, most frequently external ones, as bases of divi- 

 sions by means of resemblances or dissemblances. It is likenesses 

 in both instances, but tn the natural one the morphological re- 

 semblances are taken in their totality; while in the artificial one, 

 external characters, often only appearances, are ^ivon weight. 

 To arrange living forms, in other words, in a natural classifica- 

 tion requires a far-reaching knowledge of morphology on the 

 part of the taxonomer; while an artificial one. although often 

 convenient in some few particulars, may be conceived by almost 

 any observer with common powers for comparison of objects. 

 All birds, for example, might, in an artificial classification, lie 

 easily placed in one group or class; lines might then be drawn 

 upon the fact (hat some birds were " land birds " and others 

 "water birds" — ignoring the matter of structure entirely — and 

 by similar reasoning make minor groups of " diving birds." 

 "scratching birds," "climbing birds," "perching birds," and so 

 on. All this can de done as a. matter of observation of habit 



