METAMOKPHOSES. 



61 



form from infancy to old age, they appear at one period 

 under a shape so diiferent from that which they finally 

 assume ; and why should they pass through an intermediate 

 state of torpidity so extraordinary ? I can only answer that 

 such is the will of the Creator, who doubtless had the wisest 

 ends in view, although we are incompetent satisfactorily to 

 discover them. Yet one reason for this conformation may 

 be hazarded. A very important part assigned to insects in 

 the economy of nature, as I shall hereafter show, is that of 

 speedily removing superabundant and decaying animal and 

 vegetable matter. For such agents an insatiable voracity is 

 an indispensable qualification, and not less so unusual powers 

 of multiplication. But these faculties are in a great degree 

 incompatible. An insect occupied in the work of reproduc- 

 tion could not continue its voracious feeding. Its life, there- 

 fore, after leaving the egg, is divided into three stages. In 

 the first, as larva, it is in a state of sterility ; its sole object 

 is the satisfying its insatiable hunger ; and, for digesting the 

 masses of food which it consumes, its intestines are almost all 

 stomach. This is usually by much the longest period of its 

 existence. Having now laid up a store of materials for the 

 development of the future perfect insect, it becomes a pupa ; 

 and during this inactive period the important process slowly 

 proceeds, uninterrupted by the calls of appetite. At length 

 the perfect insect is disclosed. It now often requires no 

 food at all ; and scarcely ever more than a very small quan- 

 tity ; for the reception of which its stomach has been con- 

 tracted, in some instances, to a tenth of its former bulk. Its 

 almost sole object is now the multiplication of its kind, from 

 which it is diverted by no other propensity ; and this im- 

 portant duty being performed, the end of its existence has 

 been answered, and it expires. 



It must be confessed that some objections might be thrown 



too, as well as snakes, cast their skin by an operation somewhat similar to that 

 in larvce. There is nothing, however, in their metamorphoses at all resembling 

 the pupa state in insects. (See, however, Von Baer's article on the Analogies 

 of the Transformations of Insects and the Higher Animals in the Annales des 

 Sciences Nat.) According to Mr. J. V. Thompson, both the common barnacles 

 and many Crustacea undergo metamorphoses, but to what extent these changes 

 take place in the latter does not seem clearly ascertained. 



