662 ` The Colors of Animals and Plants. [November, 
whence would arise the preservation of those varieties whose 
longer wings, bodies, and antenne, and slower flight, rendered 
them noticeable, — characters which now distinguish the whole 
group in every part of the world. Now, it would be at this stage 
that some of the weaker-flying Pieride which happened to re- 
semble some of the Danaide around them in their yellow and 
dusky tints, and in the general outline of their wings, would be 
sometimes mistaken for them by the common enemy, and would 
thus gain an advantage in the struggle for existence. Admitting 
this one step to be made, and all the rest must inevitably follow 
from simple variation and survival of the fittest. So soon as the 
nauseous butterfly varied in form or color to such an extent that 
the corresponding eatable butterfly no longer closely resembled 
it, the latter would be exposed to attacks, and only those varia- 
tions would be preserved which kept up the resemblance. At 
the same time we may well suppose the enemies to become more 
acute and able to detect smaller differences than at first. This 
would lead to the destruction of all adverse variations, and thus 
keep up in continually increasing complexity the outward mim- 
icry which now so amazes us. During the long ages in which 
this process has been going on, many a Leptalis may have become 
extinct from not varying sufficiently in the right direction and 
at the right time to keep up a protective resemblance to its 
neighbor; and this will accord with the comparatively small 
number of cases of true mimicry as compared with the frequency 
of those protective resemblances to vegetable or inorganic objects 
whose forms are less definite and colors less changeable. About 
a dozen other genera of butterflies and moths mimic the Dan- 
aide in various parts of the world, and exactly the same ex- 
planation will apply to all of them. They represent those species 
of each group which, at the time when the Danaide first acqu ed 
their protective secretions, happened outwardly to resemble some 
of them, and have by concurrent variation, aided by a rigid ope 
tion, been able to keep up that resemblance to the present day. 
(To be concluded.) 
sult Mr. Bates’s 
original paper, Contributions to an Insect-Fauna of the Amazon Valley, oa 
Transactions of the Linnean Society, vol. xxiii., p. 495; Mr. Trimen’s aie ois 
vol. xxvi., p. 497; the author’s essay on Mimicry, etc., already referred me ses, 
in the absence of collections of butterflies, the plates of Heliconide and Leptali . 
in Hewitson’s Exotic Butterflies, and Felder’s Voyage of the Novare ne 
examined, $ 
* 
