DIPTEEA. 



CHAPTER I. 



The last Order of Insects is the Diptera, i.e. those insects which 

 have only two transparent wings, incapable of being- folded. 

 In strict accuracy, these insects really have four wings, but one 

 pair is undeveloped, and only represented by two little projec- 

 tions called halteres, or balancers. These will be described 

 presently. The wings have generally at their bases a pair of 

 little winglets, or ' alulets,' which are not separate wings, but 

 merely appendages of the true wings. The tarsi have five 

 joints. There are other distinctions, but these are amply suffi- 

 cient for our purposes. 



Now, let us give a short time to the examination of the 

 halteres. If the reader will take any Dipterous insect — the 

 commo7i Daddy-long-legs is as good an example as can be 

 found — and look at the thorax with a magnifying glass, he will 

 see that the development of that part of the body is very 

 curiously managed. 



The front division, or the ' prothorax,' is very small, so small 

 indeed that it is scarcely more than a collar, just large enough 

 to afford support to the first pair of legs. The middle division, 

 or 'naesothorax,' is enormously large, the reason being that it 

 has to carry not only the middle pair of legs, but the upper 

 pair of wings, and must therefore afford space for the muscles 

 which move those organs. And, as in the generality of the 

 Diptera, the wings are moved with singular rapidity, it is 

 evident that their muscles must be proportionately lapge. The 

 last division, or ' metathorax,' is larger than the prothorax, and 

 much smaller that the mesothorax. It carries the hind pair of 



