246 THE SPICULIFERA. 



size and of variable form^ according to the species of 

 insect whose egg has been deposited in the place. 

 Within these excrescences, which are sometimes of a 

 fleshy or spongy, and sometimes of a woody nature, 

 the larvae of these minute creatures live and feed ; and 

 here also, after attaining their full size, they undergo 

 their transformation to the pupa state, and await their 

 final metamorphosis, protected by its walls from the 

 vicissitudes of the weather, and from many of the 

 other varied ills to which insects are exposed. Ex- 

 crescences of this kind are well known as galls, and 

 from their habits, the insects of this group have re- 

 ceived the name of Gallicola, or inhabitants of gaUs. 

 Each gall is generally the habitation of a single larva, 

 but many of the larger kinds enclose several cells, 

 each of which contains a grub. 



As a general rule, each species of Gall-fly infests 

 not only a particular plant, but also a particular part 

 of the plant, and its puncture always produces the 

 same form of excrescence. The oak, of all our trees, 

 is the most subject to the attacks of these insects, and 

 almost every part of it nourishes a particular species 

 appropriated to itself. The leaves, in summer, are 

 often covered with the smooth round galls of Cynips 

 Quercus folii, and several other species also deposit 

 their eggs upon the leaves. The well-known oak- 

 apples are produced by the puncture of another spe- 

 cies (C. Quercus teriyiinalis) upon the young shoots 

 of the oak. Another species (C. Quercus pedunculi) 

 attacks the catkins of the male flowers, producing 

 small round galls, which, being attached to the pe- 

 duncle of the catkin, closely resemble a bunch of 

 currants ; and another (C. Quercus gemmos), by punc- 

 turing the young terminal buds, produces a singular 



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