the same remark will apply to every one of the cases that we have 
had under observation. Not only in the instances of resemblance 
between Insects of different Orders, as between Hymenoptera and 
Diptera, but also where the affinity is much closer and the diver- 
gence in structure is comparatively slight, we never encounter 
the smallest indication that the process of assimilation involves 
anything but superficial and easily recognisable features. Less 
obvious external characters and all the details of internal orga- 
nisation remain unaffected, except in so far as they may assist 
the superficial resemblance. If there is any significance at all in the 
phenomena under discussion, we seem led to the conclusion that 
they must stand in some relation or other to the faculty of vision. 
Akin to the foregoing point is the fact that in the establishment 
of a mimetic resemblance, the same broad and visible effect is often 
produced by different means. It has been established, for example, 
. that although certain South American Pierines, as we have seen, 
are excellent copies of the red, yellow and black Ithomiines and 
Heliconiines of the same region, the red and yellow pigments of 
the Pierines are chemically distinct from those of their models. A 
still more striking illustration of the same principle is due to an 
interesting investigation by Prof. POULTON. There is a large 
number of cases in which the resemblance is in great measure 
dependent on an acquired, or rather secondary, transparence of an 
originally opaque wing. It might have been expected that this 
quality of transparence had been in all cases brought about in the 
same manner, the visual effect being practically identical. But 
POULTON has shown that « whereas in the Ithomiines the transpa- 
rence is due to an alteration in shape and diminution in size of the 
minute scales which normally clothe the wing, in the Pierines the 
same effect is produced by a mere diminution in size, the shape 
remaining unaltered. The Danaines [which enter into this com- 
bination] owe their transparence to a reduction in the number of 
the scales, not to any alteration in shape or in size; while in the 
associated Moths the effect results, not from any change in size, 
shape or number of the scales, but from the fact that the individual 
scales themselves become transparent, and are sometimes set up 
vertically, so as to let the light pass between them » (the Author, in 
« Nature » for October 31st, 1907, p. 675). Here then we have 
another proof that the assimilation does not extend further than to 
easily obvious features. 
A further point that soon impresses itself upon the observer of 
the phenomena of mimicry is this : that the resemblances which 
