368 ZOOLOGY 



is the first and only appearance of this sex in the life-history 

 of the Phylloxera. The male is devoid of mouth and aliment- 

 ary canal; it fertilises the female, which soon after lays a 

 single fertilised egg, the so-called "winter egg." This is 

 deposited in some crevice or crack in the bark of the vine ; in 

 the spring a " stock-mother " hatches out of this egg and makes 

 her way to the young buds of the vine, and inserts her pro- 

 boscis into the upper surface of a 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— ^aZZico^a — 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 radicola. 



The complicated life-history of this form may be expressed 

 by the following table : 



Eoot-infesting form $ (radicola) 



Eoot-infesting foi-m, 2nd generation 



Root-infesting form, 3rd generation, etc. 



Winged form $ 



Large egg Small egg 



Wingless female Male 



j ^1 



I 

 Winter egg 



Stock-mother 



Gall_-produoing form Sj. (gallicola) 



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



Eoot-infesting form 9 (radicola) 



Family Coocidae (Scale Insects, Bark Lice, Mealy Bugs). — 

 The members of this group differ a good deal both in their life- 

 history and in their structure, and very frequently the two sexes 

 of the same species are markedly different in appearance and 

 habits. The antennae are usually long, eight to eleven joints, and 

 filiform ; the tarsus is two-jointed. The males alone amongst 



