84 
INTRODUCTION TO 
within the space of thirty (lays. From five they 
extend to nine or ten, the latter number having been 
observed in the tiger moth, ( Ckelonia caja.) But 
the great majority of insects do not undergo this ope- 
ration oftener than three or four times. The cater- 
pillars of butterflies are usually limited to the for- 
mer of these numbers, those of moths to the latter, 
but among moths many other exceptions occur 
besides the one mentioned above. The proximate 
cause, as already intimated, of this moulting, is 
the more rapid expansion of the body than of the 
shin, which, in consequence, soon exceeds the capa- 
city of its envelope: the latter, it is true, admits 
of a certain degree of distention, but a few fixed 
points on its surface, as well as the rigidity of the 
part enclosing the head necessary to give support 
to the masticating organs, prevent it keeping pace 
with the growth of the body. The larva ceases 
to eat when the change is approaching, and, during 
this temporary suspension of its ordinary employment, 
the fat lying immediately beneath the outer skin 
is absorbed, a circumstance which greatly hastens 
the crisis by abstracting the moisture from the skin 
and shrivelling it, while, at the same time, it tends 
still further to dilate the internal parts. The colours, 
being dependent in a great measure on the fresh- 
ness and moisture of the skin, also become dull 
and confused. The only motions made by the larva 
are occasional contortions and undulatory movements 
of the segments, which ultimately produce a complete 
separation between the exterior skin and the new 
