40 
BRITISH GALLS 
shown in Fig. 4. The brown flaps of epidermis that remain 
after it has fallen away are depicted in Fig. 5. These are 
supposed to resemble the valves of an oyster-shell—hence 
the popular name, which is not very appropriate. The 
falling of the galls caused a constant pattering noise in the 
woods throughout August and September, resembling that 
of rain drops. They fell in such numbers that on a square 
inch of road beneath an Oak on August 21 I counted 
thirteen of these galls. The wasp that emerges from the 
“oyster” gall is the Andricus ostreus. According to Adler, the 
sexual form is Neuvoterus Aprilinus, but Mayr holds other 
views, and Beyerinck claims to have bred N. Aprilinus from 
Fig. 2—Axillary Bud of the Common Oak with Gall caused 
BY THE PRESENCE OF THE LARVA OF AndHcitS fcCUndatOY. (l/2.) 
Fig. 3—Staminate Flowers with Galls resulting from the 
presence of the Larvae of Andricus pilosus. (3/1.) 
galls caused by the presence of the larvae of Andricus 
solitarius. 
In some instances the galls of one generation are rarely 
seen, whilst those of the alternate one are very common. 
In the majority the apparently rare galls are the little spring 
forms on buds and staminate flowers, and it may be con¬ 
cluded that they escape observation through their minute¬ 
ness, and the fact that they are usually situated on the 
higher branches. 
The hairy catkin gall and its alternate, the well-known 
artichoke gall, illustrate this. The former is said to be 
rare in Britain. It appears on the staminate flowers in 
