
’ 
Dec. 22, 1870] 

outweighs the ‘‘ determination of its foraminiferal affinities by a 
point no larger than a pin’s head,” and I feel assured that when- 
ever impartial geologists take the question up the fossil itself will 
become extinct. T. MELLARD READE 
Blundellsands, Liverpool, Dec. 12 
The Difficulties of Natural Selection 
Mr. WALLACE’s frankacknowledgment, for which I thank him, 
that he had in his two previous letters misunderstood my line of 
argument in what I consider one of the most important points at 
issue between us, absolves me from the task of again defending 
myself from charges of error and self-contradiction. As, moreover, 
Mr. Wallace has not accepted my challenge ‘‘ to explain the nature 
of the intelligence which was operative in the creation of man, 
and which is a principle unknown in the rest of the organic 
world,” it is impossible to pursue futher this branch of the ques- 
tion. All naturalists will look forward with the most intense 
interest to Mr. Darwin's long-promised work on Natural Selec- 
tion as applied to Man. There are, however, one or two subsi- 
diary points raised in the discussion, to which I shall be glad of 
the opportunity of briefly referring. Mr. Stebbing, objecting 
to my attempted parallelism between mimicry and instinct, says 
that ‘‘it can hardly be said to be proved” that the extraordinary 
resemblances occasionally found in the vegetable kingdom are 
not protective or mimetic. I certainly think it can be. When 
we find an almost absolute identity between the foliage of a 
plant belonging to Africa and another growing in South 
America,* we are certainly justified in saying that one has not 
imitated the other, and that it gains no protection from the 
resemblance. Mr, Carvalho again makes merry over what he 
calls ‘‘my” argument, that imperfect imitation is, to all appear- 
ances, not beneficiul in the cases published by Mr. Weir. The 
argument isnot mine. I simply recount the observations made 
by practical entomologists, undertaken at the suggestion of Mr. 
Wallace himself. Mr. Carvalho’s argument, which follows, is 
an instance of how, when a theory is once adopted, every con- 
ceivable fact may, by its too zealous advocates, be twisted to 
support it. Had these twig-like caterpillars been rejected by 
birds, it would have been considered a triumphant proof of the 
theory of Natural Selection ; the fact that “they are eaten with 
great relish,” we are told is equally ‘‘ really in its favour” ! 
Westminster Hospital, Dec. 17 ALFRED W. BENNETT 
Is Mimicry Advantageous ? 
THE discussion of mimicry among butterflies, in the recent 
numbers of this Journal, has brought to my mind some consider- 
ations which seem to have been overlooked by those who have 
treated the subject. 
Of the fact of mimicry there can be no possible doubt, and in 
some instances it is even more striking than has been asserted. 
Fox instance, in North America, Messrs. Walsh and Riley have 
pointed out the resemblance between Danais Archippus and 
Limenitis Misippus ; they might also have shown that in the 
extreme southern states where Z. AZisifpus occurs, and D. 
Archippus is replaced by D. Berenice, the colour of the mimetic 
Limenitis deepens neaily or quite to the tint of the southern 
Danais. 
But of how much actual benefit to the mimetic species is this 
so-called ‘* protective ” resemblance? It seems to occur where 
it can be of the least possible advantage to the species. The 
great sources of destruction here, as in all groups of animals, are 
in early life. How large a proportion of the eggs that are laid 
by butterflies ever finally produce imagines? Let those answer 
who have attempted to follow their history in their native 
haunts. My experience leads me to believe that, at the very least, 
nine-tenths — perhaps ninety-nine hundredths — never reach 
maturity. Hymenopterous and dipterous parasites beset them 
at every step; the eggs, although so small and often heavily 
ridged, cannot escape the ovipositors of the tiny Pteromali ; 
while in attempting to breed caterpillars taken in the field, the 
chance is so greatly against the evolution of a butterfly, that 
hymenopterists actually choose this method of supplying dheir 
cabinets. “Of two hundred larve of Pieris Brassice,” Mr. 
Drewsen, of Denmark, writes to me, ‘‘I obtained only twenty 
pupe ; all the rest were attacked by A/icrogaster glomeratus,” 
and my own attempts with the larvae of Pyrameis Adalanta, both 
in America and Europe, have been even more unavailing. 
These caterpillars seem to be peripatetic banquetting halls of 
Microgasters and Tachine. 
* See NaTuRE, Vol, ii, p. 70. 
NATURE 

| at concealment. 
147 
Now it isa curious fact that while the globular egg of Limenitis 
Misippus, with its deeply-pitted shell, defended by long filamen- 
tous spines, is constantly attacked by parasites ; and the gro- 
tesque, hump-backed, strangely-coloured caterpillar of the same 
species is likewise infested to an extraordinary dezree, I have 
been unable to discover by very careful search any evidence 
that the egg or larva of Danais Archippus is ever pierced by a 
parasite ; yet the egg is not small and only lightly ribbed, and 
the caterpillar large, fleshy, smooth-skinned, and gaily banded, 
living on the widely-separated leaves of Asclepias, with no attempt 
The abundance of the imago of the Danais is 
then due quite as much to the immunity of the egg ard larva from 
the attacks of parasites, as to any freedom it may itself enjoy 
from pursuit by insectivorous birds. 
Although I have hunted butterflies for fifteen years, I confess I 
have never seen one in a bird’s bill, and my faith in that method 
of lessening their numbers is very slight. Birds, too, must be 
their greater foes in earlier life ; and the chances of living, which 
are certainly against them before they take wing, seem afterwards 
rather in their favour, at least, until they have accomplished their 
mission. 
Tf, then, such an extraordinary element as Mimicry is to be 
summoned to the aid of Natural Selection, and can perform its 
task in such a masterly manner, why has it been made to waste 
its energies upon unimportant material? If the object of the 
resemblance be protection, why does not the unfortunate cater- 
pillar of the Limenitis mimic the more favoured larva of the 
Danais ? 
I cannot now consult the writings of Messrs. Wallace and 
Bates, nor do I remember their statements respecting the abun- 
dance of the mimetic species compared to that of its normal 
congeners. In my own country Limenitis Misippus is, as a 
general rule, more common than Z. Urszda, but the difference in 
their numbers is not very marked. It is by no means as great as 
one would expect had Mimicry in the imago state so strong a 
protective power as has been assumed. Two closely allied 
species,* occupying the same geographical area, do not often 
occur in the same abundance, whatever be the cause ; and the dis- 
parity in numbers in these two species of Limenitis is no greater 
than occurs in many instances where mimicry plays no part. 
Cairo, Egypt, Nov. 9 SAMUEL H, SCUDDER 
Nepenthes 
Tue allusion to Nepenthes in Mr. Buckton’s interesting article 
in a late number of NaTuRE, on the liquid secreted by this and 
other plants, prompts me to place on record a few facts regarding 
that genus, at which I have just arrived, alter monographing 
the Pitcher-plants for the ‘‘ Prodromus Systematis Vegetabilium ” 
of De Candolle ; a work of which the publication is suspended, 
owing to the siege of Paris. 
The genus Wefenthes extends from Madagascar on the west 
to N.E. Australia, the Louisiade Archipelago, and New Cale- 
donia on the east ; embracing within these limits, thirty species, 
most of which have well marked characters in the pitcher, but 
which, with only two exceptions, present a wonderful uniformity 
in the structure of both flower and fruit. It has two foci of 
maximum development ; the Malay Peninsula(including Sumatra), 
and Borneo, in both of which localities the species are not only 
more numerous, but more gigantic than in any other country, 
No fewer than twenty-one species inhabit these two countries, 
of which thirteen are common to both; but, what is very 
remarkable, the intervening island of Java contains but one re- 
presentative of the genus, and that a totally different species from 
either the Bornean or the Malayan ; thus confirming the fact first 
brought to light by the Dutch naturalists, of the close biological 
relationship between the two former localities, to the exclusion 
of Java. Only one species has a wide range, the V. phy/lamphora, 
which extends from Sumatra to Borneo, Amboyna, China, &c., 
but is absent from the island of Java. 
Proceeding from the Malayan islands westwards, we find one 
species in east Bengal, more allied to the Javanese than to any 
other ; another in Ceylon, the old 4. desti/latoria of Linnzeus (a 
name long usurped in our gardens by the Bengal plant), which 
presents the first departure from the typical structure of the genus, 
having a spreading paniculate inflorescence ; a character shared 
by those in Madagascar and the Seychelles. Proceeding further 
west to the African islands, we find still further deviations from 
the type, which now extend to the structure of the seed and 
*L. Misippus and L. Ursula can with difficulty be separated in their 
earlier stages, although so unlike in their perfect forms. 
