DIPTERA. 137 



mounted in balsam, a high power being used to ex- 

 amine them. One of them forms a long and slender 

 bristle (seta) or tongue, furnished with distant mi- 

 nute teeth. On each side of this is a flattened seta, 

 with two rows of teeth on the edges ; these are the 

 lancets, and when not in use these organs are inclosed 

 in two jointed sheaths. Outside these are two re- 

 presentatives of jaws, or maxillae (b), each having a 

 jointed feeler or palp (a) arising from it ; the probable 

 use of the palps being to feel the position of the 

 skin, so that the animal may be able to adjust the 

 lancets at a proper distance for puncture. 



The eggs of the flea are often visible within the 

 body of the parent ; and when this is crushed, they 

 are more distinctly seen, of various sizes, and con- 

 tained within a long tube, which is the ovary or egg- 

 bag. The eggs are laid by the animals upon carpets, 

 woollen garments, or in the cracks of dirty floor- 

 boards ; they are just perceptible to the eye as white 

 oblong specks, and they may always be found on the 

 rug when a cat is kept in the house. When hatched, 

 they give rise to a minute white worm-like maggot, 

 or larva (fig. 30), having a 12-jointed body, with two 

 rudimentary antennae and two slightly curved hooks 

 appended to the last joint. The mouth-organs of the 

 larva are adapted for biting, and not for sucking, as 

 in the perfect animal, the jaws or maxillae being dis- 

 tinctly toothed. When they have acquired full 

 growth, which takes place in about twelve days in 

 warm weather, they spin around themselves a little 

 silky cocoon, and become transformed into a chrysalis 

 or pupa ; and from this, in about a fortnight, the per- 

 fect insect escapes. 



DIP'TERA (819, twice, irrepov, wing). This, which 

 forms the fifth Order of Insects, consists of the two- 

 winged insects, or flies, as the house-fly, the blue- 

 bottle, the gnats, &c. 



MUS'CID^E. The house-fly, and the blue-bottle or 



N3 



