DI.MOUIMIIS.M AND I'OLV.MOUPIIIS.M. 317 



siK'li a.s Kiiryinus, tUinillur to every outdoor entomologist, wherein the 

 female, instead of being of nearly the same color as the male with some 

 distincticjus in the marginal bands, is of so very pallid a hue as to strike the 

 <)l)Herver at once. The contrary is true as regards the female of Jasoniades 

 glaucus and the male of Cyaniris pseudargiolus, in which, in certain parts 

 of the country, a dark form of the sex with nearly uniform l)rown up])er sur- 

 face is to be found. 



But dimorphism by no means stops here, for we have in some of our 

 other butterflies quite as striking or even more striking peculiarities. Take 

 for instance the case of Polygonia interrogationis. Here is an insect where 

 there are two veiy distinct forms in each sex, and in each of which the 

 sexes are readily distuiguished by the coloration of the wings ; they differ 

 in the bri":htness and variejjation of the lower siu'face of both wino-s, and 

 the obscurity of the upper surface of the hind pair ; that is to say, there 

 are four sets of individuals, which may be separated quite as readily as 

 most closely allied butterflies, and more so than a great many acknowledged 

 species of the best studied faunas. Nor is this by any means the whole 

 statement of the case ; these two types, bred from eggs laid by the same 

 parent, not only differ in the markings of the wings, but also in their form 

 and in the structure of the genitalia ; in fact, we have two sets, perma- 

 nently distinct from each other, and to which we can only not apply the 

 name of species, because we know them to have the same parent. Now 

 butterflies seek their own kind for mating and nothing more is needed to 

 establish these forms as good species, than that each should persistently 

 seek its own mate. Indeed, one can hardly help surmising that they 

 already do so to a considerable extent, and that this is an instance of an 

 almost formed species, beyond which it is almost impossible to go without 

 becoming one. Between this condition and that of some other species, in 

 which the sexes do not differ and there is very little vai'iation, there is 

 almost every grade of difference, so that we may fairly imagine that we 

 know one means by which species are originated. Here, perhaps, if any- 

 where among butterflies, we ought to suspect that physiological selection, 

 the province of which is so w^ell insisted upon by Romanes, is beginning to 

 play its part in the formation or rather the differentiation of species ; since 

 besides the colorational marks which may enable the sexes to choose their 

 mates with discrimination, we have the first steps toward those changes in 

 the organs ancillary to generation which everywhere mark absolutely dis- 

 tinct forms, and are safeguards against admixture. The case of Iphiclides 

 ajax is even more striking ; nor has the story half been told of the muta- 

 tions and polymorphism of Cyaniris pseudargiolus ; but since a new ele- 

 ment is here brought to view, in which dimorphism is exhibited by alternate 

 broods of the same insect, we refer the reader for further particulars to the 

 8ecti(m upon that subject. 



