140 



FOREST ENTOMOLOGY. 



Acller : arranges the species in the four following groups viz. : 

 I. Neuroterus. III. Dryophanta. 



IT. Aphilothrix. IV. Biorhiza. 



In attempting to give some detailed account of the various species 

 of oak galls whereby the galls themselves may be recognised in the 

 forest and the insects verified after hatching in confinement, it is 

 obvious there are several ways open for adoption. 



We might follow a botanical method and describe the galls on buds, 

 leaves, fruit, and roots ; or we might adopt an entomological course, 

 and describe and compare the various species as found on the respect- 

 ive parts of the tree. But we shall adhere 

 to the arrangement of Adler, because we may 

 then follow the commonest species and have 

 a direct bearing on a most important biological 

 law viz., the alternation of generations. 

 Firstly, take 



1. Neuroterus lenticularis, 01. 2 (Oak- 

 spangle Gall). 



This gall is very common throughout the 

 country from July to September. The galls 

 are scattered promiscuously on the under side 

 of the leaves (fig. 130), are more or less circular, 

 and develop in July from objects resembling 

 pin-points. They are clothed with stellate 

 hairs on the upper side, but smooth on the 

 under side of the surface, pressing against the 

 leaf and very slightly attached to the leaf. They are raised in the 

 centre, tapering to thin edges on the leaf, and with the outer edge 

 lying flat on the leaf. If specimens which lie on the ground over 

 winter be measured in March, just before the flies hatch out, it will 

 be found that they have the same breadth as in autumn, but have in- 

 creased considerably in thickness. At this time of the year they will 

 measure about 4 mm. in breadth and 2 J mm. in thickness. 



1 Alternating Generations; p. 8. Translated by Dr Strattoti. 1894. 



2 The figures 1 and la represent alternating species. Thus 1 alternates with 

 la, 2 with 2a, and so on. It should be noted also that the generations marked 

 la, 2a, &c, produce insects of both sexes, whereas insects in the generations 

 marked 1, 2, &c, are all females. 



Fig. 130. Galls of Neuro- 

 terus lenticularis (oak- 

 spangle gall). 



