1420 THE STORY OF THE UNIVERSE 



it never acquires wings, but is stated to do so 

 sometimes in warmer climates. The Heteroptera 

 can not exactly be said either to sting or bite. The 

 jaws, of which, as usual among insects, there are two 

 pairs, are like needles, which are driven into the 

 flesh, and the blood is then sucked up by the lower lip, 

 which has the form of a tube. This peculiar struc- 

 ture of the mouth prevails throughout the whole 

 order; consequently their nutriment consists almost 

 entirely of the juices of animals or plants. The 

 Homoptera agree with the Heteroptera in the struc- 

 ture of the mouth, and in the metamorphoses. They 

 differ principally in the front wings, which in Ho- 

 moptera are membraneous throughout, while in the 

 Heteroptera, the front part is thickened and leathery. 

 As in the Heteroptera, however, so also in the Ho- 

 moptera, some species do not acquire wings. The 

 Cicada, celebrated for its chirp, and the lanthorn 

 fly, belong to this group". So also does the so-called 

 cuckoo-spit, so common in English gardens,which has 

 the curious faculty of secreting round itself a quan- 

 tity of frothy fluid which serves to protect it from 

 its enemies. But the best known insects of this group 

 are the Aphides or plant-lice; while the most use- 

 ful belong to the Coccidae, or scale insects, from one 

 species of which we obtain the substance called lac, 

 so extensively used in the manufacture of sealing- 

 wax and varnish. Several species also have been 

 used in dyeing, especially the cochineal insect of 

 Mexico, a species which lives on the cactus. The 

 male coccus is a minute, active insect, with four 

 large wings; while the female, on the contrary, never 



