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have a real affinity, the genera to which they belong being throughout very similar in 
colours and markings, and all equally nourishing, to the similar adaptation of all to the 
same local, probably inorganic, conditions. The selecting agent, which acts in each 
locality by destroying the variations unsuitable to the locality, would not in these cases 
be the same as in Leptalis ; it may act, for anything we know, on the larvae ; in other 
respects, however, the same law of nature appears, namely, the selection of one or more 
distinct varieties by the elimination of intermediate gradations *. The conditions of life 
of these creatures are different in each locality where one or more separate local forms 
prevail, and those conditions are the selecting agents. With regard to the Leptalides, 
I believe we may be said to know these conditions. To exist at all in a given locality, our 
Leptalis Theonoe must wear a certain dress, and those of its varieties which do not come 
up to the mark are rigidly sacrificed. Our three sets of Leptalides may be compared to 
a variable flowering plant in the hands of a number of floriculturists, whose aims are dif- 
ferent, each requiring a different colour of flower, and attaining his end by " roguing " 
or destroying all variations which depart from the standard. 
It may be remarked that a mimetic species need not always be a rare one, although 
this is very generally the case ; it may be highly prolific, or its persecution may be in- 
termitted when the disguise is complete. 
The operation of selecting agents, gradually and steadily bringing about the deceptive 
resemblance of a species to some other definite object, produces the impression of there 
being some innate principle in species which causes an advance of organization in a 
special direction. It seems as though the proper variation always arose in the species, 
and the mimicry were a predestined goal. This suggested the only other explanations 
that I have heard of, namely, that there may be an innate tendency in the organization 
to become modified in a given direction — or that the parent insect, being powerfully 
affected by the desire of concealment from the enemies of its race, may transmit pecu- 
liarities to its offspring that help it to become modified, and thus, in the course of 
many generations, the species becomes gradually assimilated to other forms or objects. 
On examination, however, these explanations are found to be untenable, and the appear- 
ances which suggest them illusory. Those who earnestly desire a rational explanation, 
must, I think, arrive at the conclusion that these apparently miraculous, but always 
» 
Some of the close resemblances amongst the Heliconida themselves seem to be kept up by their varying in a 
precisely similar way. There is a very singular instance in three species of three different genera, Melineea, Mecha- 
nitis (Mothone), and Heliconius, which are all, in East Peru, orange and black in colour, and in New Granada 
orange, black, and yellow. This seems to be a case of coincident, simple variation ; for if three forms are quite alike 
in colours, it is conceivable that they may vary alike when placed under new conditions by migration. Our Lepta- 
lides have been shown not to vary precisely like their models ; and therefore the case just quoted does not throw any 
difficulty in the way of the explanation I have given ; but it is a very extraordinary one. 
I have not thought it necessary to mention cases of close resemblances in insects which are only accidental, or which 
are explicable by the blood- relationship or affinity existing between the species which display them. Some orders of 
insects contain an almost infinite variety of forms, and it will not be wonderful, therefore, if species here and there 
be found to resemble each other, although inhabiting opposite parts of the earth, and belonging to widely different 
families. Such analogies are accidental, and can have nothing at all to do with the evidently intentional system 
of resemblances, carried on from place to place, which I have discussed. Some cosmopolitan families present very 
similar species in all parts of the earth ; it can scarcely be necessary to say that close resemblances between New and 
Old World forms in these cases are resemblances of affinity, and not mimetic analogies. 
