DimorpMsni and Polymorphism in Butter fiies. 25 



studied, and the facts which I shall set forth are the 

 common property of lepidopterists. 



Under the title dimorphism, I have included sexual 

 diversity, although this is frequently treated of separately 

 under the term antigeny. 



You are all aware that many animals exhibit striking 

 differences between the sexes, and this is true of many 

 butterflies, some of which differ much more between the 

 sexes than do those of the same sex of different species, 

 and some differ so greatly that you would suppose them 

 to belono; to different 2;enera, while others differ so little 

 that it takes an entomologist of some experience to 

 separate them. Not only is there great range of degrees 

 of difference, but also the variety of ways in which they 

 differ seems almost endless. 



And not only do the different genera vary greatly 

 in this way, but even within the limits of a single genus 

 you may have species in which the sexes are practically 

 identical, species in which they differ slightly, others, 

 differing more strongly, and so on till we reach a species 

 where the sexes are so unlike that they might easily be 

 taken for different species or even different genera. Such 

 a group is the genus Argynnis, a genus very typical of the 

 Palearctic and ISTearctic fauna. 



The ismaller species, such as Myrina, Montinus, &c., 

 which Dr. Scudder separates under the generic name 

 Brenthis, are practically identical in the sexes, though 

 there is a slight difference in the point of origin of one of 

 the nervules of the hind wing. 



In the majority of the species the males may be said to 

 have the ground color fulvous, while in the females it 

 inclines to luteous, but in a few there is a very striking 

 diversity between the sexes. 



Argynnis Cybele, which is quite common in this locality, 

 is a very good example of the majority, though the 

 contrast is, perhaps, greater than in the average, while 



