700 



CLASS IV. INSECTA. 



leaf. The irritation thus set up causes the formation of a hollow gall on 

 the under surface of the leaf, which opens to the exterior on the upper 

 surface. The stock-mother lays eggs, and her offspring gallicolae give 

 rise to new galls, but ultimately some of them descend to the ground, 

 burrow beneath it and attach themselves to the roots, and thus become 

 radicolae. 



The complicated life-history of this form may be expressed by the 

 following table : 



Root-infesting form 9 (radicola) 



I 



Root -infesting form, 2nd generation. 



I 



Root -infesting form, 3rd generation, etc. 



Winged form 9 . 



I 



Large egg 



I 



Wingless female 



Small egg 



ilt 

 I 



I 



Winter egg 



Stock-mother 



Gall-producing form 9 (gallicola) 

 Gall-producing form 9 , 2nd generation, etc. 



! 



Root-infesting form 9 (radicola). 



Fam. 8. Aleurodidae. Minute. Four white, mealy wings. Antennae 

 7 -segmented, the second segment long. These small insects are usually 

 found on the under surface of leaves. The two sexes are about equally 

 developed and both are winged. There are two genera Aleurodes and 



Aleurodiscus with some 150 species. 

 Aleurodes brassicae is common on cab- 

 bages in Britain. 



Fam. 9. Coccidae. The eggs give 

 rise to larvae, which in those cases 

 that have been investigated, are alike ; 

 but later development is quite differ- 

 ent in the two sexes. The male 

 passes through pupal stages, and 

 finally emerges as a minute insect with 

 only one pair of wings, anal cerci, and 

 with the mouth atrophied. The female 

 becomes very much larger than the 

 male, and never acquires wings ; the 

 antennae and legs usually degenerate, 

 the latter sometimes disappearing en- 

 tirely. Mouth-parts are present in the 

 adult females, which are very fre- 



FIG. 445. Coccus cacti, a female 

 b male (after Bunneister). 



