X PREFACE. 



greatest difficulty in deciding questions of this kind is in the case of 

 insular forms, among which occur every possible degree of difference 

 between related forms inhabiting different islands, so that it not only 

 becomes largely a matter of individual judgment as to which should 

 be given specific and which subspecific rank, but furthermore the dis- 

 tinction made must, in the case of any author, necessarily be more or 

 less arbitrary, since no "hard and fast rule" for determining such 

 questions seems possible. 



As observed before, the more familiar one becomes with the subject 

 through the medium of specimens representing continuous geographic 

 sequence of localities the fewer in number really distinct species become, 

 and what have long been considered such resolve themselves, one by 

 one, into a connected scries of subspecific forms, each representing a 

 definite geographic area of more or less marked peculiarities of topog- 

 raphy, climate, or other physical features. Such forms are fixed, or 

 "true," over territory of uniform physical character, the intergrades 

 coming from the meeting ground of two such areas. Such a group of 

 conspecific forms may aptly be compared to the colors of the solar 

 spectrum, which form a graded scale from red, through orange, yellow, 

 green, and blue, to violet, with intermediate hues of greater or less 

 number, according to the nature of the case requiring their indication 

 by name. These colors of the spectrum, though imperceptibly run- 

 ning into one another, are obviously distinct, and the necessity of recog- 

 nizing them by name has never been questioned. 



•To carry the comparison still further, a certain species may include 

 six subspecies or conspecific forms, which for convenience may be 

 designated by the subspecific names rnhra,^i(in'a)itiaca,Jlava,viridis, 

 cyanea, and violaceu. Intermediates between these might be designated 

 as ruhro-aurantiaca (or rmrantiaco-ruira, according to which form the 

 intermediate most resembles), aurantiaGO-jiava (or flamo-aurantiava)^ 

 flavo-olridis, niridi-cyanea. and cyaneo-viohicea^ i. e., red-orange (or 

 orange-red), orange-yellow (or yellow-orange), yellow-green, green- 

 blue, and blue-violet of the color scale. The necessitj' for such a 

 nomenclature is just as great in zoology (and botany) as in chromato- 

 graphy; and to ignore this necessity is neither scientific nor sensible, 

 but on the other hand is nothing less than suppression or perversion 

 of an obvious truth. The only question that can possibly exist in the 

 mind of those who ha\^e this matter to deal with is the degree of dif- 

 ference which should be recognized in nomenclature, and in this respect 

 there is excuse for more or less difference of opinion, according to one's 

 ability to discern differences and estimate the degree of their con- 

 stancy, the extent and character of material studied, and the amount of 

 time which has been devoted to its investigation. No doubt many of 

 the forms which the author has recognized as subspecies in the present 

 work may appear trivial to others, especially those who have not had 



