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, Gosdart, 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 

 ^ZZ it begins to feed with avidity, and increases much in size. The 

 larva of the SpJiinx ligiistri, at the moment of leaving the Qgg, 

 Aveighs 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 14.1-^^ 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 



