120 THE AMERICAN NATURALIST [Vol. LVI 



the various grades of clieeks form a series moving in one 

 direction, the ultimate outcome of which is the two-barred 

 and finally barless types. And Miss Jones points out 

 that it does not ''necessarily follow that because the 

 interaction of these several factors produces an apparent 

 epistatic series, the mutations producing the various 

 grades of checking should have occurred in any particular 

 order." 



And here, to my mind, is the crux of the matter. In 

 order to have what may legitimately be termed orthogen- 

 esis, do the underlying mutations have to occur in any 

 particular order? Is not the very fact that, instead of 

 existing as a medley of wholly unrelated elements, certain 

 characteristics of organisms, such as color markings, can 

 frequently be arranged as parts of a definite pattern or 

 as stages in a general process — does not this in itself 

 indicate directional variation? When one sees in its 

 incipiency, as it were, in one species a character which 

 has attained to an advanced expression in a kindred 

 group, especially where there are intermediate expres- 

 sions of the same characteristic in other related species, 

 is not this indicative of a general trend in variation? 

 For instance, is not the tendency toward the formation 

 of '' eye-spots " in the plumage of the pheasants hinted 

 at even in the greenish-black iridescence so often visible 

 in the tail feathers of the common rooster — is not this 

 tendency the expression of what in last analysis must be 

 a germinal bias? To be sure, this bias finds different 

 ranges of expression in different species : as eye-spots on 

 the wing-feathers in some species, on the body-feathers 

 in others. In one species they may occur as a single row 

 of ocelli, in another as two rows, across the tail. And 

 it is obvious that certain of these patterns have not been 

 derived directly from others, since they appear in what 

 are clearly collateral lines. Nevertheless, the tendency to 

 form ocellations is present in many if not all species of 

 this great group. We know nothing of the order in which 

 the mutations occurred which brought about any partic- 



