138 INSECTS. 



meat-fly, are both species of the genus Musca, be- 

 longing to this family, the former being Musca do- 

 mes tica, the latter Musca vomit or' ia. Both these 

 insects are seen to be wonderfully constructed when 

 minutely examined, and they possess considerable re- 

 semblance in general structure. 



On examining the head of the house-fly (PI. X. 

 fig. 17) under a low power, and as an opake object, 

 the observer will be struck with the remarkable ap- 

 pearance presented by the two eyes, which are large, 

 placed one on each side of the fore part of the head, 

 and composed of very numerous little eyes closely 

 packed together, or they are compound, as it is called. 

 The use of this compound structure is evidently to 

 enable the little animal to see in all directions with- 

 out moving the head and eyes. Each little eye has 

 a lens to bring the rays of light emanating from 

 objects to a focus upon a nerve. The packing of the 

 eyes together gives rise to their angular form or 

 their straight sides, each of the little surfaces or facets 

 being hexagonal, or bounded by six sides (fig. 33). 

 In front of and between the eyes are seen the two 

 small antennae ; these have three joints, the third of 

 which is larger than the rest (fig. 170), and arising 

 from near its base is a feathery bristle or seta ; these 

 structures are best seen when the antennae are pulled 

 off with a pair of forceps and mounted separately. 

 Below the antennae, and extending downwards and 

 forwards is the proboscis, or tongue, as it is called, 

 which can be entirely retracted within a pit in the 

 fore part of the head, or protruded at the will of the 

 animal. This is a very beautiful and complicated in- 

 strument, and is best examined when spread out and se- 

 parately mdunted (PL X. fig. 29). It consists of a fleshy 

 tube, dilated at the end into two lobes, which are 

 flattened beneath to form a sucking-disk. The end 

 is furnished with two solid horny lateral branches to 

 keep it expanded, and with two longitudinal tubes 



