Mr. R. Meldola on Evolution. 15% 
it. Fritz Miiller records the following exceptions :—“ There 
are here some exceptions to the rule that the imitating species 
are comparatively rare, while the imitated swarm in large 
numbers. Thus Mechanitis Lysimnia is hardly more common 
than the imitating Leptalis; and the beautiful Papilio nepha- 
lion, Godt., is here so rare that I have seen only two or three’ 
specimens last summer, whilst the imitating Huterpe tereas is: 
by far more common. But in other parts of Brazil the nume- 
rical relations of these species may be different.” 
I would add, with reference to this observation, that it is 
quite conceivable that in certain districts external conditions 
may so change that a species dominant in other regions may 
become rare or altogether extinct, while the species which 
mimics it may remain unaffected. Thus Diadema misip- 
pus, the female of which mimics Danais chrystippus, is 
found in South America, while the model Danavs is not *. 
Mr. Trimen also remarks ¢ :—‘‘ The magnificent Papilio Anti- 
machus, Drury, of which but one specimen is known to 
science, is very Acreiform in habit, and is possibly an instance 
of special modification in imitation of some gigantic Acrea as 
yet unknown or perhaps extinct.” Papilio Zalmoxis also, as 
I am informed by Mr. A. G. Butler, probably mimics some 
unknown or extinct gigantic Acrea. Many cases are known 
in which a butterfly 1s obviously a mimic, but its exact model 
is unknown}. I am disposed to believe that such instances 
show us the precess of mimetic resemblance in actual progress. 
For example, many species of H/ymnias resemble species of 
Euplea ; but it is impossible to name the precise species of the 
last genus which in each case serves as a model. In these 
cases it is more reasonable to suppose that the mimicry of the 
Elymnias is in course of perfection, than to assume that the 
species which they imitate have become extinct. It is also 
* This species (D, musippus) is stated to occur in Guiana on the autho- 
rity of Boisduval. My friend Mr. A. G. Butler has just informed me 
that a large male from Formosa, in which the Danaiform characters 
are partially visible, has been lately added to the national collection. 
Here we have an interesting case in which mimetic characters originally 
acquired by a female butterfly are probably in course of transmission to 
the male. 
+ Trans. Linn. Soc. vol. xxvi. p. 503. I learn that probably two other 
specimens have been obtained since the above was written. 
_ { For numerous instances of imperfect mimicry see papers by A. G. 
Butler :—“ A Monograph of the Lepidoptera hitherto included in the 
Genus Elymnias,” Proc. Zool. Soc. June 6, 1871; also on Protogonius, 
ibid. Dec. 2, 1873, and Jan. 19, 1875, Mr. Neville Goodman points out 
(Proc. Camb. Philos. Soe., Feb. 12, 1877) that ¢vmperfect resemblances are 
arguments in favour of the production of the phenomenon through the 
action of natural selection. 
