LEPIDOPTERA. 265 
to descend too quickly ; it descends by stages; it stops in the air 
when it pleases. Generally it only descends at most about one 
foot at a time, and sometimes only half a foot or a few inches, 
after which it makes a pause more or less long as it pleases.” It 
is in this way that the caterpillars let themselves fall from the 
top of the highest trees. They remount again with no less ease. 
Let us listen to Réaumur’s description of the means em- 
ployed by this caterpillar to ascend these heights. Figs. 260 and 
261, drawn as the three preceding ones from the plates in Réau- 
mur’s Memoir, help us to follow the explanation given by the 
illustrious naturalist of the evolutions of our little acrobat :— 
“To remount,” says Réaumur, “the caterpillar seizes the thread 
between its jaws, as high up as it can catch it; as soon as it has 
done this it twists its head round, lays it over on one side, and 
continues to do so more and more every moment. Its head seems 
to descend below the last of the scaly legs which are on the same 
side as that to which it is inclined. The truth is, however, that 
it is not its head which descends, the part of the thread which it 
holds between its jaws is a fixed point for its head and for the rest 
of its body: it is that portion of the back corresponding with its 
scaly legs which the caterpillar twists upwards; the consequence 
is that it is the scaly legs and that part of the body to which they 
belong which then ascend. When the last pair of legs are just 
over the jaws of the caterpillar, one of its legs, viz., that which 
‘is on the side towards which the head is inclined, seizes the thread 
and brings it over to the corresponding leg on the other side, 
which is advanced to receive it. If the head then raises itself, 
which it will not fail to do immediately, it is in order that it may 
seize the thread at a higher point than that at which it seized it 
at first ; or, which is the same thing, the head, and consequently 
the whole body of the caterpillar, is found to have ascended to a 
height equal to the length of the thread which is between the 
place where its jaws seized it the first time and that where they 
seized it the second time. Here then is, so to say, its first step up- 
wards. Hardly has the caterpillar taken this than it takes a second. 
If you were to seize the caterpillar when it had arrived at 
the end of its upward journey, you would sce a packet of threads 
huddled together between the four hindmost of the scaly legs. 
