318 MOTIONS OF INSECTS. 
form this motion by means of a pectoral process or mu- 
cro. These animals having very short legs, when laid 
upon their backs, cannot by their means recover a prone 
position. To supply this seeming defect in their struc- 
ture, Providence has furnished them with an instrument 
which, when they are so circumstanced, enables them 
to spring into the air and recover their standing. Ifyou 
examine the breast (pectus) of one of these insects, you 
will observe between the base of the anterior pair of legs 
a short and rather blunt process, the point of which is 
towards the anus. Opposite to this point, and a little 
before the base of the intermediate legs, you will disco- 
ver in the after-breast (postpectus) a rather deep cavity, 
in which the point is often sheathed. 'This simple appa- 
ratus is all that the insect wants to effect the above pur- 
pose. When laid upon its back, in your hand if you 
please, it will first bend back, so as to form a very ob- 
tuse angle with each other, the head and trunk, and ab- 
domen and metathorax, by which motion the mucro is 
quite liberated from its sheath; and then bending them 
in a contrary direction, the mucro enters it again, and 
the former attitude being briskly and suddenly resumed, 
the mucro flies out with a spring, and the insect rising, 
sometimes an inch or two into the air, regains its legs and 
moves off. ‘The upper part of the body, by its pressure 
against the plane of position, assists this motion, during 
which the legs are kept close to its underside. Cuvier, 
when he says that man and birds are the only animals 
that can leap vertically?, seems to have forgotten this 
leap of Elaters, which is generally vertical, the trunk be- 
ing vertically above the organ that produces the leap. 
2 Anat. Comp. i, 498. 
