Aphilotrix corticis. 37 



cambium layer, with a central chamber in which the 

 larva lies. At the beginning of the cold weather gall 

 formation is arrested, to be resumed and rapidly com- 

 pleted in the following spring. In May the thickening 

 of the bark increases very much, distinct roundish 

 swellings are formed, which burst and disclose the 

 beautiful red conical galls. They grow 4-5 mm. above 

 the level of the bark, and their bases are rooted in the 

 substance of the wood. In June they reach maturity, 

 and in autumn the fly is fully formed, but passes the 

 winter in the gall ^ 



[The leaf-vein gall is found in June on Q. sessiliflora. 

 Inquilines. Synergiis aptcalis and Ceroptres arator. 

 Parasite. Megastignius dorsalisl\ 



7. Aphilotrix corticis. L.^ 

 Gall. These galls are found in the bark of thick oak 

 roots, or in the swellings that form around old injuries 

 to the bark, like those usually seen where boughs have 

 been sawn off. When fresh the gall appears of a hemi- 

 spherical or oval form, covered by a sappy, reddish 

 yellow, or ochrey envelope. The real larva chamber 

 lies under the level of the bark and penetrates by 

 conical points into the substance of the wood. The 

 bell-shaped upper half dries after maturity and falls 



' These, like other galls, are greatly exposed to the attacks of 

 various parasites (species of Tor^^mus and Synergus), and it is in- 

 teresting to observe how the gall has indirectly evolved a means of 

 protection. The red sappy envelope secretes a sticky fluid which is 

 eagerly sought after by ants, and that they may enjoy this nectar 

 undisturbed, they build with sand and earth a perfect dome over the 

 galls, and in this way provide the inhabitants with the best possible 

 protection against their enemies. 



[^ Cynips corticis, Hartig. Andricus corticis, Mayr.] 



