154 

and the animals have not strength to move the instrument, so 
that ‘both ploughs and ploughmen succumb, and the antedi- 
luvian implement of the ryot is found to be the only feasible 
” 
one. 
Some idea of the damage done to vegetation by locusts in 
tropical countries may be gathered from the following account of 
a raid made by them in an East Indian cotton plantation. The 
means adopted to repel them was by recourse to the discordant 
sounds of native music—horns, tom-torns, and pipes—aided by 
the waving of flags and branches of trees. These measures, un- 
doubtedly, saved the produce ; for, judging by the performance 
of the very small number that succeeded in gaining admission to 
one of the finest fields unobserved, had a full complement effected 
a lodgment, one hour would have sufficed to strip every tree of 
its leaves, though the foliage was abundant, and the plants in 
one field from five to six feet high. The immunity which the 
native Indian cotton enjoyed from the attacks was  consi- 
derable, considering the avidity with which they devoured the 
exotic descriptions, and, true to their early traditions, the Egyp- 
tian was evidently an especial favourite. Some of the swarms 
that passed over the country at that time were exceedingly 
numerous. The arrival and settlement of one mighty mass was 
a remarkable sight. Whatwas first observed was a sort of haze 
on the verge of the horizon, in a long line, as if a steamer 
had passe, and its smoke was rising into vapour; this was 
some hours before the insects arrived. The cloud gradually 
thickened, and rose higher as they approached. When 
they got fairly overhead the air became darkened as if 
night was setting in, it being yet mid-day, and the peculiar 
sound which accompanied their flight resembled that of 
the rustling of the leaves of the peepul tree when agitated 
by light winds; but it is not until they have settled down that 
any idea can be formed of the immensity of their numbers, and 
the early dawn, before sunrise has warmed them into life and 
motion, is the time to witness this most extraordinary sight. In 
the instance now referred to the appearance the face of the country 
wore would be best described by supposing that a tolerably heavy 
fall of snow had taken place, only that the colour of it wasa 
light brown, and this extended for miles, as far, indeed, as the eye 
could reach. Trees were favourite perching-ground for the night, 
and the manner in which they contrived to crowd upon them, 
piles over piles, concealing every vestige of leaf and branch, gave 
the trees a singular appearance, At one spot a stout and wide- 
spreading branch of a banyan tree had snapped at its stem from 
the incumbent weight of the insects. 
Ricit mines of gold and silver are being daily discovered in 
the State of Tulima, in Columbia, according to late advices. 
A RECENT number of the American Journal of Chemistry 
contained the following story of the first introduction of the 
stereoscope to the savants of France. The Abbé Moigno took 
the instrument to Arago, ani tried to interest him in it; but 
Arago unluckily had a defect of vision which made him see double, 
so that on looking into the stereoscope he saw only a medley of 
four pictures. The Abbé then went to Savart, but he was quite 
as incapable of appreciating the thing, for he had but one eye. 
Becquerel was next visited, but he was nearly blind, and conse- 
quently cared little for the new optical toy. The Abbe, not 
discouraged, called next upon Puillet, of the Conservatoire des 
Arts et Métiers. He was a good deal interested in the descrip- 
tion of the apparatus, but unfortunately he squinted, and there- 
fore could see nothing in it but a blurred mixture of images. 
Lastly, Biot was tried, but Biot was an earnest advocate of the 
corpuscular theory of light, and until he could be assured that 
the new contrivance did not contradict that theory, he qwoz/d not 
see anything in it, Under the circumstances, the wonder is that 
the stereoscope ever got fairly into France. 
NATURE 

aS ee eae 
| Dec. 22, 1870 

MIMICRY AND HYBRIDISATION * 
OME time since I had occasion to study with care, for the 
purposes of a work on which I am engaged, the pheno- 
mena of mimetic analogy made known by Mr. Bates, which have 
lately formed the subject of discussion at the British Association, 
and in the pages of NatruRE, in which I observe with pleasure 
that one of our body, Mr. A. W. Bennett, has borne an honour- 
able part. Neither he nor any of the gentlemen who have written 
on the subject, have, however, so far as has come under my 
notice, brought the point to its real issue. They have accepted 
battle on the field on which Mr, Bates has placed it, and although 
they may have achieved a victory over him, they have not suc- 
ceeded in rescuing the subject from its obscurity. He may be 
wrong without their being right. I am not surprised at their 
having been led to accept his premises ; when I first approached 
the subject I did the same; but the longer I live and the more 
extended my experience becomes, the more surely do I find that 
when a theory looks shaky and unsound, the place to look for 
the flaw is not in the upper story, but in the basement. It is in 
the foundation that the crack will almost invariably be found, T 
am sure it is so here. 
Mr. Bates found in the Valley of the Amazons a number of 
species of a Northern tribe of butterflies, wearing the colour and 
form of a Brazilian tribe, and so like in their varieties and strains 
that they obviously represent some different phenomenon from 
the ordinary one of mere difference in species. To account for 
this he devises a theory on the Natural Selection plan. The 
Brazilian tribe has a bad smell, and birds and insects of prey 
consequently do not feed upon them, and the Northern tribe, in 
the course of their variation in the dark, accidentally produce 
one something like the Brazilian one, which produces others in 
the same direction by Natural Selection, until’ the mimics are 
brought to perfection. Every inch of the ground he goes over 
here is mined and unsound—the bad smell has not been observed 
in North America where similar mimicry occurs —birds and in- 
sects of prey hunt by sight and not by smell, and the various 
communications on the subject in NATURE point out a variety of 
other insuperable objections. But my object is not so much to 
show that a friend and entomological brother has been seduced 
by a ‘‘bad smell” to go on a wrong scent, like a good dog after 
a red herring, but to find out the true explanation of the pheno- 
menon. 
The explanation seems to me to be simply Hybridisation ; 
but before committing myself to it, as there were one or two 
points on which I was not sure how far the phenomena corre- 
sponded with those of hybridisation in plants, | applied to my 
friend’ Mr. Isaac Anderson Henry for information upon them, 
and he has sent me a paper (for the Scientific Committee of the 
Horticultural Society), as well as some other information, which 
enables me now to say that there is not a phase or a fact in the 
mimicry in question, for which I cannot produce the exact 
counterpart in the hybridisation of plants. 
In the first place the mimicked and the mimickers are 
always found together, and even the mimickers of varieties 
are only found beside the varieties that they mimic. Now, 
it is plain that if the resemblances be due to hybridisation, 
it is inevitable that the two must always be found together, at 
least in the first instance. It may be that after the hybrids are 
established and advanced into the position of actual species, 
the species (7.2, the parent and offspring) might diverge from 
their primary locality, the one to the right and the other to the 
left, and so cease to be found together ; but this must be an 
after act, and consequently an exception. The natural condition 
is to find both together, and so they are always found together. 
But this would not be the natural condition if the mimicry were 
produced by Natural Selection. The same enemies are found over 
thousand of miles, and the same kind of enemies over tens of 
thousands; and there is no advantage to be gained by mimicking 
one variety of Danais more than another. The same advan- 
tageous results would be obtained by mimicking in the east the 
form that prevails in the west, or in the north the form that 
prevails in the south, but the imitation of each variety is 
limited to the district which it inhabits, however narrow and 
restricted it may be. Natural Selection, therefore, fails entirely 
to account for the localisation of the mimickers of varieties. 
In the next place the mimicked occur always in over- 
whelmingly greater numbers than the mimickers. Mr. Bates 
says :—“ The Ithomice (Danaids) are all excessively numerous in — 
* This paper was originally presented to the Scientific Committee of the 
Horticultural Society (Dec. 7, 1870), but has not yet been published elsewhere. 

