CHAP. VIII 



BUGS 



533 



the mouth-organs of the individual are of one form throughout 

 its life. In this latter fact, coupled with another, that the 

 young are not definitely different in form from the adult, 

 Bugs differ widely from all other Insects with sucking-mouth. 

 They agree with the Orthoptera in the facts that the mouth does 

 not change its structure during the individual life, and that the 

 development of the individual is gradual, its form, as a rule, 

 changing but little. In respect of the structure of the mouth, 

 Orthoptera and Hemiptera are the most different of all the 

 Orders. Hence, Hemiptera is really the most isolated of all the 

 Orders of Insects. We shall subsequently see that, like Orthoptera, 



FIG. 255.JSiisthenes 

 pratti (Pentato- 

 midae). China. A, 

 Xymph : a, case of 

 anterior, b, of pos- 

 terior wing ; c, ori- 

 fices of stink- 

 glands ; B, tlie 

 adult Insect. 



the Order appeared in the Palaeozoic epoch. Although a very 

 extensive Order, Hemiptera have for some incomprehensible 

 reason never been favourite objects of study. Sixty years ago 

 Dufour pointed out that they were the most neglected of all the 

 great Orders of Insects, and this is still true ; our acquaintance 

 with their life-histories and morphology especially being very 

 limited. 



There is probably no Order of Insects that is so directly con- 

 nected with the welfare of the human race as the Hemiptera ; 

 indeed, if anything were to exterminate the enemies of Hemiptera, 

 we ourselves should probably be starved in the course of a few 

 months. The operations of Hemiptera, however, to a large ex- 

 tent escape observation, as their mouth-setae make merely pricks 

 that do not attract notice in plants ; hence, it is probable that 



