STRUCTURE OF INSECTS. 317 



6. Imago, or Perfect Insect. 



THE process which nature has followed in the 

 developement of the structure of insects, has for 

 its object the gradual hardening and consolida- 

 tion of texture, and the union and concentration 

 of organs : for we find that the segments which 

 were at a distance from one another in the larva, 

 are approximated in the perfect insect, and 

 often closely tied together by ligaments : and in 

 other cases, adjoining segments cohere so as to 

 form but a single piece. Thus the number of 

 separate parts composing the solid fabric is con- 

 siderably diminished. Other segments, again, 

 fold inwardly, forming internal processes, and 

 adding to the extent and complication of the 

 skeleton. 



The integuments of perfect insects, being de- 

 signed to be permanent structures, are thicker 

 and more rigid than those of their larvae, 

 and are formed of several layers, in which the 

 component parts of the integuments of the larger 

 animals may readily be distinguished. Their 

 rigidity does not, like that of shells, arise from 

 the presence of carbonate of lime ; for they con- 

 tain but a small proportion of this material : and 

 whatever calcareous ingredient enters into their 

 composition is in the form of phosphate of lime. 



