258 



Arthropoda. 



occupies tte greater portion of the small body. These eggs rest dui-iag the 

 winter, and in spring develop into the first virginal generation. Besides the 

 fertilised eggs, a number of apterous parthenogenetic females persist during the 

 winter, in the larval stage, firmly attached to the roots of the vines.* 



Fig. 215. Phylloxera vastatrix. 1 Young female of one of the apterous parthenogenetie 

 generations. 2 Older ditto, from the ventral surface. 3 Adult female of the winged 

 generation. 4 Female of true sexual generation (the ovum shows through the skin). 

 5 Male. All the figures of equal magnification. — After Comu. 



(c.) Vajt-ious Aphides produce characteristic galls on trees and bushes, 

 Chermes abietis, for instance, by sucking at young pine shoots causes cone- 

 like galls by shortening and broadening the needles. Pemphigus spirothecx 

 forms a spiral gall on the petioles of poplars ; crumpled or saccular galls are 

 caused on elm leaves by various Aphides, and so on. 



4 The Scale-insects (Coccidx) axe allied to the Aphides, but differ- 

 from them in various respects. Sexual dimorphism is usually very mai'ked. 

 The female is cumbrous, apterous, and short- legged, and is usually somewhat 

 motile only in youth, later becoming fixed to one place, where the eggs are laid. 

 Soon after oviposition the coccus dies, but the body which has gradually shrunk 

 to a thin arched shield remains as a protection to the eggs. Very often the- 

 female is covered dorsally by a continuous layer of wax secreted by the skin 

 glands; sometimes the eggs are suiTOunded by fine wax thi'eads. The male 

 possesses well- developed fore -(vings ("with few veins), whilst the hind wings are- 

 rudimentai-y and like halteres or altogether absent ; the mouth-parts are 

 rudimentary. The larvae resemble young females. It is a very remarkable 

 fact that the males (not the females) pass through a resting pupa-stage^ 



* In addition, it may be noticed that in exceptional cases, wingless parthenogenetic. 

 females may occur attached to the -vine leaves, where they produce galls. 



