102 BRITISH APHIDES. 



I have often witnessed tbe rapid births of these 

 insects. These young, which form the fourth genera- 

 tion, are very active, they run swiftly and have long 

 rostra, by which they suek up the sap, and thereby grow 

 rapidly. They course up and down the elm twigs and 

 show their presence by the plentiful tufts of cotton 

 with which they powder the leaves. In Belgium, near 

 Spa, I have seen the elms hoary with this cottony 

 substance, and then the shaking of a bough produces a 

 shower of liquid exudation and white flocks. 



The fifth generation appears also to be apterous; 

 but the sixth once more shows pupal forms and 

 discloses the corresponding imago towards the end of 

 June and throughout July. 



These are ''les pupiferes " of Lichtenstein. Except 

 that they are usually much smaller, they do not greatly 

 differin appearance from the earlier alate insects. They 

 roam far and wide on the wind currents : those which 

 discover suitable quarters establish themselves. Ac- 

 cording to Riley, they particularly choose the bark, 

 and there they give birth to the seventh and last gene- 

 ration — the perfect sexes. These are very diminutive, 

 and on that account for a long time they were over- 

 looked by Entomologists. They are of various shades 

 of colour, from bright yellow to orange and red. 



The males, so far as my experience goes, are born 

 with rostra, but these organs disappear after a moult. 



This degradation of type in the sexes is remarkable, 

 and it has been commented upon by Lichtenstein, 

 E-iley, Low, and others. It also obtains in other species 

 of Fem^liigincB and Schizoneurince. 



The oviparous females are, on the other hand, born 

 mouthless, and thus are incapable of obtaining nourish- 

 ment. The ovum nevertheless enlarges, perhaps from 

 the imbibition of w^ater through the parent. 



After retiring into the hollows of the elm bark, the 

 females lay their single eggs, or else die without ex- 

 truding them, which nevertheless live, as before 

 noticed, to recommence the cycle of the ensuing year. 



