OF EPPING FOREST. 169 



galls appear in May, maturing at the end of the month. During 

 June the sexual generation of flies emerges, oviposition taking 

 place on the root (sometimes, according to Adler, in the leaf bud). 

 The females may be apterous, but the males are always winged. 



OCCURRENCE IN EPPING EOREST. 



Biovkiza apteva. Fairly plentiful and probably abundant, 

 but less noticeable on account of their situation. 



Biorhiza tenninalis. \'ery abundant. Occur singly or two or 

 three together, many growing from the terminal buds. They are 

 found also growing from the axillary buds. The}^ vary greatly 

 both in size and colour, and are very subject to parasites and 

 commensals of almost every insect order. 



Some trees were simply a mass of galls, which remain on the 

 tree in many cases during the greater part of the winter. First 

 appearance noted, May loth. 



Genus TRIGONASPIS {Hartig). 



The Agamic Forms of this genus are wingless like the 

 ■corresponding forms of the genus Biorhiza, but they are all much 

 smaller in size ; the head is also dilated behind the eyes, and the 

 ovipositors differ considerably. The sexual form is very well 

 marked and entirely different to the agamic generation, the 

 wings being large and well formed and the abdomen red in 

 colour. There is only one British species at present known. 



It has not been ascertained for what reason there is an egg 

 resting stage in the agamic generation. The eggs are deposited 

 in the leaf by the sexual flies, at the end of May or beginning of 

 June, but the larvae do not leave the eggs, and gall growth does 

 not commence, until September. 



The reason for the apterous condition of the agamic 

 generation is probably due to the fact that the perfect insects do 

 not require their wings before oviposition as the eggs are 

 deposited in the adventitious buds on the trunks of the trees, 

 usually near the ground, or in buds on young stems from six 

 inches to a foot in height, which grow up around the trees 

 from acorns which have fallen to the ground and germinated. 

 It is quite the exception to find galls at any great distance from 

 the ground. 



The same thing applies to those Biorhiza tenninalis females 

 -which are apterous, namely, that they would appear to be 



