714 THE BUTTERFLIES OF NEW ENGLAND. 



Each slew a slayer and in turn was slain, 

 Life living upon death. So the fair show 

 Veiled one vast, savage, grim conspiracy 

 Of mutual murder, from the worm to man, 

 Who himself kills his fellow. 



We may apply the same reasoning to two kinds of butterflies subject 

 naturally to the same class of enemies, i. e., living in the same region 

 and flying at the same time. If one has the slighest advantage over the 

 other in the fight for life, by being for instance distasteful to one class of 

 common enemies, so that these forbear to attack him after experiment or 

 by instinct (the result of ancestral experiments) ; and there be among the 

 less favored flock, here and there, an individual which under circum- 

 stances favoring it, such as distance or shadow, may more often than it8 

 fellows be mistaken by the enemy for one of its distasteful neighbors 

 through its possession of a little more than usual of a certain tint on a 

 part of the wing, a little larger spot here, or more of the semblance of a 

 band there, — how small soever this difference may be, it must, by the 

 very laws of natural selection, be cherished, perpetuated. Increased by 

 slow but sure steps. Nor is there any limit to its increase, except its 

 absolute deception of the enemy. So long as there is the slightest advan- 

 tage in variation in a definite possible direction, the struggle for existence 

 will compel that variation. Knowing what we now know of the laws of 

 life, mimicry of favored races might even have been predicted. 



It is to be presumed that the actual colors found in a mimicking 

 butterfly are, with rare exceptions, such as existed somewhere in the 

 ancestral form. In the case of our own mimicking Basilarchia, for 

 example, whose orange ground tint is so totally at variance with the gen- 

 eral color of the other normal members of the group, it will be observed 

 that all the normal species possess some orange. Without this as a pre- 

 cedent fact, such perfect mimicry might perhaps never have arisen. Indi- 

 viduals among the normal species vary somewhat in this particular, so 

 that it is easy to suppose that some of the original archippus with more 

 orange than usual may have escaped capture on occasion from this cause. 

 From such a small beginning, such as one may now see every year in B. 

 astyanax, sprang doubtless the whole story, and we now find a butterfly 

 which has for a ground color of both surfaces of the wings an orange 

 which is the exact counterpart of that of Anosia plcxippus : by reason of 

 which in all probability it enjoys a freedom fi-oni molestation comparable 

 to that attributed to plexippus, so that it ventures more into the open 

 country than its allies, and thus gains a wider pasturage and surer subsis- 

 tence. 



It would seem then to be plain tiiat all cases of j)rotective coloring and 

 mimetic form come under one and the same law and have been produced 



