THE FLY. 47 



the last pair of legs and halteres upon the metathorax, 

 or last subdivision of the chest. 



The most important of these members, looking at 

 the habitat of the Fly, are Tmdoubtedly the wings. 

 They consist, as you are well aware, of a pair of mem- 

 branous expansions; each wing is composed of an 

 upper and lower transparent membrane, and between 

 these two layers the blood-vessels and respiratory 

 tubes [trachem) ramify, so as to form a beautifiil net- 

 work for the support of the extended membranes. 



You will perhaps be somewhat surprised to hear 

 that the wings of our little Fly, to whose structure you 

 may never have devoted a single moment's thought 

 during your lifetime, have been so carefully investi- 

 gated, and received so much of the anatomist's atten- 

 tion, that not only has each branch or ' nervule,' as 

 these ramifications (PI. VI. fig. 1, a) are termed, but also 

 each intervening portion of the transparent membrane 

 has been deemed worthy of receiving a distract de- 

 signation. To enumerate these would be to trespass 

 beyond the limits and intention of this little treatise ; 

 but we mention the fact, in order to show how much 

 there is to be learnt in creatures of even the most 

 humble character. 



We may here also observe, that near the root of the 

 wings, where these are joined to the body, there have 

 been discovered a great number of small vesicles, the 

 nature of which is still a mystery ; but as we shall 

 have occasion to describe them more fully when 

 treating of the halteres, where they are also found. 



