THE NATURE OF METAMORPHOSIS. 6$ 



adapted to the performance of new functions, but is eaually in- 

 capacitated for the continuance of some of those which it has 

 previously enjoyed. It is during this period that new parts are 

 developed, and the insect's mode of life is in consequence entirely 

 changed. Whilst these alterations are taking place in the organic 

 structures, the functions of the organs themselves are in a great 

 measure suspended, and the condition of the insect becomes that of 

 the hybernating animal. Respiration and circulation are reduced 

 to their minimum, and the cutaneous expenditure of the body is 

 then almost inappreciable, even by the most delicate tests. Thus 

 a pupa of Sphinx ligiistri which in the month of August, imme- 

 diately after its transformation, weighed 71 "i grains, in the month 

 of April following weighed 67 '4 grains, having thus lost only 37 

 grains in the long period of nearly eight months of entire absti- 

 nence. The whole of this expenditure, therefore, had passed off 

 by the cutaneous and respiratory surfaces. But when the changes 

 in the internal structures are nearly completed, and the perfect 

 insect is soon to be developed, the respiration of. the pupa is 

 greatly increased, and the gaseous expenditure of its body is 

 augmented in the ratio of the volume of its respiration, which is 

 greatest the nearer the period of perfect development. Thus, in 

 the same insect in which the diminution of weight was so triflino- 

 during eight months' quiescence and abstinence, it amounted in the 

 succeeding fifty-one days to nearly half the original weight of the 

 pupa, since the perfect insect, immediately after its appearance on 

 the 24th of May, weighed only thirty-six grains. This increased 

 activity of function is attended with a correspondent alteration in 

 the general appearance of the pupa, 



" In the Sphinx all the parts of the future imago become more 

 and more apparent on the exterior of the pupa case, the divisions 

 into head, thorax, and abdomen are more distinctly marked ; the 

 eyes, antennae, and the limbs appear as if swollen, and ready to 

 burst their envelope, and the pupa gives signs of increasing 

 activity by frequent and vigorous contortions of its abdominal 

 segments. The naked pupa, or nymph, in which, as we have 

 seen, all the parts of the body are free, and encased only in a 

 very delicate membrane, acquires a darker colouring and a firmer 

 texture ; while the species which undergo their metamorphosis 



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