DIPTERA. 141 



&c., takes place ; so that when the insect emerges 

 from the shell of the chrysalis, it has attained its 

 highest state of development, and forms the imago or 

 perfect insect. It may be remarked here, that when 

 insects pass through the three states of larva, pnpa, 

 and imago, they are said to undergo complete me- 

 tamorphosis. There is not a more curious object 

 than that presented by the young fly contained in its 

 case, as seen on carefully cutting away portions from 

 one end of the case of the chrysalis. The body and 

 head are quite white, with beautiful blood -red eyes. 



Most persons must have noticed another kind of 

 house-fly, having the wings more widely separated 

 than in the common fly, and moving more slowly 

 through the air. This is Stomoxys catcitrans. The 

 proboscis of this fly (PL X. fig. 18) differs from that 

 of the house-fly in being longer, more bent, and but 

 little expanded at the end ; also in being provided 

 with two long setae, one forming a slender sharp 

 lancet, the other being somewhat stouter, and form- 

 ing its sheath. The fly is thus enabled to pierce the 

 flesh and suck the blood. 



CULIC'ID^E. We will now say a few words about 

 the gnats, which are old favourites for microscopic 

 examination. The three states of larva, pupa, and 

 imago must be considered separately. 



The imago or perfect form is well known. The 

 males are easily distinguished from the females by 

 the difference in structure of the antennae, which 

 in the males (PL X. fig. 10, head) are very beauti- 

 fully plumose or feathery, whilst in the females 

 (fig. 11) the hairs are very short the long proboscis, 

 or rostrum, or bundle of biting-organs forming the 

 striking feature ; this difference is immediately evident 

 to the naked eye. 



The antennae of the males (fig. 10 a) consist of 

 numerous small joints, from each of which arises 

 a ring of long hairs, giving the appearance of a tuft 



