166 

instances in various parts of the world in which Pafi/ios of cer- 
tain groups are the objects of mimicry. Although Mr. Scudder 
has never seen a bird capture a butterfly, others have been more 
fortunate, and that they are thus captured very largely in the 
tropics is certain. It is not improbable, from the rarity of 
mimicry in the temperate zone, that the few cases which exist 
may have been produced under the more favourable climatal and 
organic conditions of the semi-tropical epochs anterior to the 
glacial period. ALFRED R. WALLACE 
The Difficulties of Natural Selection 
THE papers read by me before the Entomological Society “On 
the Relation between the Colour and the Edibility of Lepi- 
doptera and their Larva” having been noticed and commented 
upon by Mr. A. W. Bennett and others in Nature, I have 
deemed it desirable to offer a few remarks on the subject. 
The object I had in making the experiments was to ascertain 
whether there could be proved to exist any relation between the 
colours of larvze and their edibility. 
The disciples of Mr. Darwin argued that the brilliant colours 
of so many male birds arose from sexual selection, and that the 
equally striking colours of flowers were but guides to insects, to 
enable them to dis'inguish, at some distance, the flowers from the 
leaves, and thus insure fertilisation by the interchange of pollen. 
Such reasons, however, were quite valueless to account for the 
bright colours of the asexual larvae of many Lepidoptera, several 
species of which are banded and striped with blue, yellow, and 
red; colours which instead of concealing them by harmonising 
with the leaves on which they feed, are often in complete contrast 
with the n. 
Now Mr. Wallace had a theory that these gaily coloured larvze 
were uneatable by birds, and that their gay colours were pro- 
tective, because if they were indistinguishable from eatable 
species, they would be seized by birds, and though rejected 
afterwards, would be so much injured that ihe probability of 
their becoming imagines would be very remote, even if they 
were not at once killed. 
This I found to be the case ; in my experiments extending over 
many years, and most carefully made with several species of 
birds, I have not met with one instance in which a strikingly- 
coloured larva was eaten. In most cases they were not even re- 
garded when thrown into the aviary, although I had several 
birds always on the watch for the eatable species, with which I 
constantly fed them; while these latter were seized immediately 
they were seen. 
The larva of the Cwucullia verbasci is conspicuously coloured 
blae and yellow, and feeds without any attempt at concealment 
on several species of Verbascum. I placed the plants in the 
aviary, and fed the Cucullize upon them until every leaf was 
devoured, and the caterpillars gnawed holes in the stem ; but 
not one was in the slightest degree injured, yet at the same time 
other larvze were greedily eaten. 
On the other hand, I found that all Jarvee were eagerly eaten 
which have soft smooth bodies and dull colours, while the hairy 
larvee are rejected entirely. 
These eatable species are protected in various ways ; some are 
nocturnal in their habits, descending to the ground during the 
day ; some feeding on the under sides of the leaves; others 
arrange their bodies in a line with the shoots of the plants and 
look like a streak of the bark ; some are of precisely the colour 
of the leaves, or even of the coroila of the plant on which they 
feed; others roll themselves up in leaves, the larve of the 
Geometride are often exactly like twigs, with the terminal and 
side buds imitated. 
This latter resemblance is so complete that, after being thirty 
years an entomologist, I was deceived myself, and took out my 
pruning scissors to cut from a plum-tree a spur which I thought 
I had overlooked. This turned cut to be a larva of a Geometer 
two inches long. I showed it to several members of my family, 
and defined a space of four inches in which it was to be seen ; 
but none of them could see that it was a caterpillar, Surely this 
was a case of protective mimicry. 
All the eatable larvze agree in not moving when there appears 
the least danger, and very rarely moving at all during the day. 
Even if there were no cases of protective mimicry in the larval 
states of Lepidoptera, I do not think that would be any argument 
against the existence of such in the perfect state. It appears to 
me rather that as so few specimens become imagines in propor- 
tion to the eggs produced, the more need is there that these few 
should survive, 
NATURE 



| Dec. 29, 1870 

I cannot, therefore, agree with Dr. Scudder in thinking that 
mimicry has been supposed to exist where it is least wanted, viz., 
in the perfect state of Lepidoptera. Nor can I coincide with 
Mr. Bennett that it is a matter of indifzrence to the supporters 
of the theory of Natural Selection whe her twig-like caterpillars 
are eaten by birds or not. My poitt is that they are often so like 
twigs that they are passed over as such by insectivorous birds, and 
that the closer the resemblance the better their chance of escape. 
I believe myself that Mr. Darwin’s theory will survive, and 
even be benefited by, the criticisms of its opponents ; but what [ 
do dread is the injury it may receive from the false arguments of 
some of its illogical supporters. 
Lest I may unwittingly place myself in the latter category, I 
will bring my remarks to a close. J. JENNER WEIR 
6, Haddo Villas, Blackheath, S.E. 

Butterflies and Birds 
A CORRESPONDENT in NATURE, Dec. 22, states that after 
fifteen years’ experience in butterfly hunting, he has never seen 
one in a bird’s bill. I was not aware the circumstance was un- 
usual, for I have frequently seen the common sparrow chase and 
capture such butterflies as V, wrtice and P. rape. It is quite a 
hare and greyhound affair, the butterfly often eludinz for some 
time the swift pounces of its pursuet, so that the hunt is a iong 
one. T, Gs; 
St. John’s College, Cambridge 
Ceratodus Forsteri 
Sir Puitip Grey EcGerron presents his compliments to the 
Editor, and would esteem it a favour if he would insert the 
following paragraphs, from two letters recently received from 
Professor Agassiz, in an early number of Nature. It will be 
gratifying to all men of science to know that the distinguished 
Professor has so far recovered fiom his late severe illness as to be 
able again to interest himself in scientific pursuits. 
Oulton Park, Tarporley 
‘ 
“* Cambridge, November 9 
“*T am slowly recovering, and find myself gradually returning 
to the ways of active life. As I wake anew to feel an interest in 
scientific pursuits, there is nothing for which I have a greater 
longing than the fossil fishes. If I could leave my house I 
would fly to you to resurce the examination of your and Lord 
Enniskillen’s collections. The recent discovery of Krefft has 
added fuel to the fire, and I feel the most intense desire to revise 
the facts bearing upon the relations of the Ganoids and Sela- 
chians in general, and more particularly those of the Coelocanthi, 
to which, from the examination of the skeleton sent me by 
Krefft, I find his Ceratodus Forster? belongs. It will no doubt 
turn out that the Dipterini are close relations. . In this connection 
I am reminded of what you once wrote to me of the teeth of 
Cienodus. Will you now have the kindness to give me all the 
particulars? I am having sections of the teeth of Ceratodus 
Forsteri and some of the tossil species made for comparison. I 
have little doubt already that this genus will turn out to be one 
of the most curious syzthetic types (I call them) in the animal 
kingdom, exhibiting characters of Placoids (Selachians) in the 
teeth, Ganoids in the scales, their embryonic characters in the 
preservation of a dorsal chord, instead of distinct bony vertebrae, 
and finally hollow bones as in birds.” 
“Cambridge, Dec. 8 
**T take it some of your naturalists will crow over what they 
will be pleased to call my stupendous mistake in referring the 
teeth of Ceratodus to the Selachians, when the fish proves to 
have large imbricated scales; and yet I never was more 
pleased than when I learned the fact, for it settles beyond dis- 
pute the existence in nature of types, to which I have long 
ago called attention, under the name of syzthetic types (see my 
Essay on Classification), but of which naturalists have thus far 
taken little or no notice. When I described the teeth of Cera- 
todus as those of a distinct genus among the Cestracionts, I was 
led to do so by appearances which secured for this association 
the assent of all naturalists. As long as the fossil teeth only 
were known, nobody questioned the relationship. Owen him- 
self, in his ‘Odontography,’ mentions the teeth of Ceratodus 
and their structure, and has not a shadow of a doubt that I am 
right in placing that genus near Cestracion ; and now comes the 
discovery that Ctenodus, a genus also referred to the Cestra- 
cionts, is based upon the dental plate of a bony fish, closely allied 
to the one recently discovered by Krefft, and referred by him to_ 
ae —_—— 
