374 Natural- Historical Collections. 
and very common in spring time. They may be held in one hand, preventing 
them with the cther hand from falling to the ground. After hesitating some 
time on the thread which they have commenced, we observe them at first deviate 
from the perpendicular line, and then at length take a more or less uncertain 
flight, to direct themselves on mounting in the air, either obliquely or perpendi- 
culariy. Care must be taken, in the first instance, by passing the hand exactly 
round the animal, that no thread exists except that below the spider, which is in- 
capable of supporting it. These observations should be made in a closed room, 
where the calm air can receive no agitation, and where we may be sure that no 
spiders’ threads can be present to assist them. Moreover, for greater precaution, 
the spiders may be brought from without in little closed bottles. By these means 
we have often repeated and varied these experiments, before many persons, and 
making use of different species of spiders. The largest bound with so sudden a 
jerk that there is no time to examine how they disappear; whilst on the contra- 
ry, the small individuals escaping less quickly, one may pass the hand before 
them, to ascertain whether a thread be darted by them, or whether, so to speak, 
they fly away without support as hardy aeronauts, of which we are convinced. 
Reflecting on the means by which these insects ascend, it seems to me very pro- 
bable, that with the assistance of the eight approximated feet, which the animal can 
cause to vibrate rapidly, a¢ swims in the air. One may conceive that these members, 
rowing by fours simultaneously on each side, strike the air like wings, and easily 
elevate the little insect, which is itself so light. Indeed this seems to be the only 
possible process. Moreover the extreme rapidity, or the inconceivable agility of 
these feet in motion, like the vibration of the wings of birds or dipterous insects 
which flutter in the air, prevents us from always distinguishing their motions. 
The objections against this explanation do not destroy the reality of a fact 
which all the world may certify ; and, besides, there is no impossibility that 
the feet beating the air, (like the swimming feet of aquatic insects strike the wa- 
ter,) may guide, in any direction of the atmosphere, beings so light, and furnish- 
ed with members so long and agile as these little spiders. Many Diptera have 
not longer nor larger wings than these feet united on each side of the spider, and 
the Pterophori have the wings as much separated as the feet. 
It is more probable that these little spiders fly with their feet, than to con- 
jecture the existence of electrical influences, or the agitation of the air, which we 
have disproved by direct observation. The instinctive vibratility of the feet in 
spiders, (a vibratility similar to that of which we observe some traces in those of the 
Phalangita after death,) appears to be abundantly sufficient to produce their sin- 
gular ascent or leaps in the air. With a similar facility they can descend ob- 
liquely, or rise to the summit of a tree, or to any other distant object, to attach 
their webs. 
But is this the only example of animals with flying feet ? They may be found 
in many others, since the wings and the fins in mammalia, birds, and fishes, are 
most of them nothing but modifications of feet. It is similar with the pteropo- 
dous mollusca, &c. | 
Nature, then, modifies the organization according to the functions with which 
she endows them, in the repnblic of every world.— Bull. des Sciences Naturelles, 
Oct. 1829. 
On the Plumage of the Dipper, (Cinclus aquaticus.)—The following observa- 
tions are communicated by our valued correspondent Mr. Macgillivray, whose 
attention has been long directed to the minute peculiarities of the feathers of birds. 
The readers of the Edin. New Phil. Journ. will recollect a valuable paper by this 
gentleman on the general subject, the sequel of which, for unknown reasons, has 
never appeared. 
The peculiarities observed by me in the Cinclus equaticus are the following = 
Land birds generally, and especially the Passeres, have certain spaces of their 
skin from which no true feathers arise, and upon which there are merely a few 
down feathers, 
