322 THE LIFE OF AN INSECT. 



an eminent naturalist, also attributes the expan- 

 sion of the wing to the flow of an aqueous fluid into 

 the nervures. M. Chabrier, a French entomo- 

 logist, having observed a fluid in the interior of 

 the nervures of the wings of insects, thinks it 

 probable that they can introduce it into them and 

 withdraw it at their pleasure, so as to facilitate their 

 unfolding. When we call to mind the force with 

 which the blow-fly, or flesh-fly, and the dragon- 

 fly, are able to expand their heads by forcing air 

 into them, we need scarcely ask for any other 

 explanation than simply that the tracheae are 

 distended with air, and by that means the soft 

 and yielding wings are made to assume their dis- 

 tended state. 



It has been mentioned, that, in the case of the 

 dragon-fly, the completion of the unfolding of its 

 wings occupies about a quarter of an hour, but that 

 sometimes it is even half an hour. The ordinary 

 period is from five to ten or fifteen minutes in most 

 insects, but it is sometimes prolonged to an hour, 

 or to several hours. Again, in others, as we have 

 already seen in the history of the emergence of the 

 gnat, and other insects, from their aquatic state in 

 the pupa, it is completed in a few seconds, and the 



