THE NATURE OF METAMORPHOSIS. 
55 
same genus, may present different grades of metamorphosis ; some 
are more fully developed when they leave the egg than others ; and 
nearly all those which are destined to lead a parasitic life suffer 
more decided changes of form at the . different stages of their 
existence than the tribes which do not live upon unwilling hosts. 
The following description of the different conditions of the 
insect is taken from Newport’s essay, already quoted : — 
“ The life of an insect that undergoes a true metamorphosis is 
one continued series of changes from the period of its leaving the 
egg to that of its assuming the perfect state. These are not 
merely from the larva to the pupa, and from that to the perfect 
animal, during which the insect gradually acquires new organs, but 
consist also of repeated sheddings of its skin, which occur at 
certain intervals, before the larva has attained its full size. These 
changes, and the circumstances connected with them, have been 
more particularly watched in lepidopterous insects, and have been 
carefully noted by many naturalists, especially by those of the last 
century, Redi, Malpighi, Goedart, Merian, Ray, Swammerdam, 
Reaumur, Lyonet, Bonnet, De Geer, and others, who concur in their 
statements respecting the manner in which these changes are 
effected. Almost immediately after the insect is liberated from the 
egg it begins to feed with avidity, and increases much in size. The 
larva of the Sphinx ligustri , at the moment of leaving the egg, 
weighs about one-eightieth of a grain ; at about the ninth day it 
casts its second skin, and then weighs about one-eighth of a grain ; 
on the twelfth day it changes its skin again, and then weighs 
rather more than nine-tenths of a grain ; on the sixteenth day it 
casts its fourth skin, and weighs three grains and a half ; and on 
the twenty-second day enters its sixth and last skin, and weighs 
very nearly twenty grains ; but on the thirty-second day, when it 
has acquired its greatest size, it weighs nearly 125 grains ; so that 
in the course of thirty-two days this larva increases about 9,976 
times its original weight. At this period it is sometimes more than 
four inches in length. But this is not the greatest weight that 
the larva attains. One specimen, which was bred in its natural 
haunts, weighed i4i x 7 o grains ; so that in this instance the in- 
sect had increased at the rate of 11,312 times its original weight. 
But great as is this proportion of increase, it is exceeded by 
