OF EPPING FOREST. 275 



have often found Audriciis feciindatvix ga.\\s rendered polythalamous 

 by a number of contained Synergid larvae. Some galls, such as 

 Andricns collaris, which naturally fall to the ground during late 

 autimm, will remain on the tree when attacked by parasites. 



The common oak Marble-gall {Cynips kollari) may often be 

 seen of smaller size and darker colour than is normally the case. 

 On cutting through one of these galls it will be noticed that 

 instead of there being one cell only in the centre of the gall, there 

 is a ring of cells present. These have been formed by Synergid 

 larvae and they will be found to have filled up and eliminated 

 the cell of the original gall-makei'. 



Cynips kollari galls often have knobs or excrescences upon 

 their surface which are caused by inquiline larvae living in the 

 gall substance. Biorhiza tevminalis galls (the common " Oak 

 Apple "j are particularly liable to parasitic infestation and are 

 inhabited by a great number of insects. As many as seventy- 

 five species have been collected from these galls, besides Acarina 

 and Araneida. 



Although some changes in the appearance of a gall, such as 

 those mentioned with regard to Cynips kollari, are due to parasitic 

 infestation, they are for the most part probably caused by some 

 substance secreted in the salivary glands of the larva, which acts 

 upon the surrounding tissue, on the juices of which the larva 

 feeds. This would account for the remarkable variety in form, 

 etc., shown by the spangle-galls of the genus Neiiroterus, since 

 the method and time of o^•ipositing are in each case apparently 

 the same. 



Oviposition and gvoti'th of the Gall. 



The piercing apparatus of a gall-fly is, as one would expect 

 to find it, of somewhat exceptional construction, the act of 

 oviposition being of extreme importance with these insects. 

 The ovipositor and its attachments take up practically the whole 

 of the interior of the abdomen when in repose. 



The plates mentioned below are paired and the whole 

 apparatus is worked by five muscles. 



It is made up of : — An anterior plate, a posterior plate and 

 a triangular plate. 



The anterior plate (Fig. 4, d) is attached to the lower end 

 of the triangular plate (r) and the base of the posterior plate (e). 



