in] SOME SUCKING INSECTS 17 



Cockroaches and grasshoppers belong to an order of 

 insects, the Orthoptera 1 , characterised by firm fore- 

 wings and biting jaws ; in all of them the change of 

 form during the life-history is comparatively slight. 

 A great contrast to those insects in the structure of 

 the mouth-parts is presented by the Hemiptera, an 

 order including the bugs, pond-skaters, cicads, plant- 

 lice, and scale-insects. These all have an elongated, 

 grooved labium projecting from the head in form of 

 a beak, within which work, to and fro, the slender 

 needle-like mandibles and maxillae by means of 

 which the insect pierces holes through the skin of 

 a leaf or an animal, and is thus enabled to suck a 

 meal of sap or blood, according to its mode of life. 

 In many Hemiptera the various families of bugs 

 both aquatic and terrestrial, for example the life- 

 history is nearly as simple as that of a cockroach. 

 It is the family of the plant-lice (Aphidae) that affords 

 typical illustrations of that alternation of generations 

 to which reference has been made. 



The yearly cycle of the common Aphids of the 

 apple tree has been lately worked out in detail by 

 J. B. Smith (1900) and E. D. Sanderson (1902). In 

 late autumn tiny wingless males and females are 

 found in large numbers on the withered leaves. The 

 sexes pair together, and the females lay their rela- 

 tively large, smooth, hard-coated black eggs on the 



1 See outline classification of insects, p. 122. 

 a I. 2 



