SOME FEATURES OF OAK GALL GROWTH. 17 
deformities thus produced are well illustrated in 
Andricus estivalis, which normally is cup-shaped ; B. 
wptera when solitary is globular. Three species of 
Neuroterus are often much out of shape on account of 
overcrowding, as may be seen on Plate LX, div. A; 
and A. Nieboldi, B. renwm and C. Kollari are at times 
subject to much distortion from the same cause. 
(b) Hnvironment.—This also requires little more than 
a passing notice. Those galls whose normal position is 
on the under-surface of the leaf do not usually 
attain their customary dimensions when on the upper 
surface. A terminal, or nearly terminally situated, 
specimen of Aphilothria callidoma is rarely as long as 
when axillary. C. Kollari is sometimes badly pinched 
in a forked twig (Plate XXXVI, figs. 9-14), or when 
bunched together in clusters (Plate XX XVIII). 
(3) Due to internal influences —(a) Parasites are the 
principal agents in causing these modifications. They 
destroy the rightful owner of the gall, and in all 
unilocular galls growth is usually arrested ; the struc- 
ture either remains a diminutive form of what it would 
have been, or. some peculiarity is accentuated, such as 
the style on A. solitarius and on C. Kollari (see Plate 
XXXIX, div. C), or increase in the number of ridges 
on Aphilothria callidoma. 
(b) Inquilines do not usually destroy the larva, but 
only live within, and feed upon, the tissues of the gall 
in company with the owner, but not in the same larval 
cavity. In the majority of galls tenanted by inquilines 
no deviation from the normal dimensions are notice- 
able. This is exceedingly well exemplified in speci- 
mens of (. Kollart on Plate XXXIX, div. B. It is 
in every way normal, yet from it there have emerged 
the rightful owner and thirty-two inquilines, but their 
combined depredations have been so great as to leave 
the exterior a mere shell. 
Of all galls, whether on the oak or any other British 
plant, none appears to harbour more parasites and 
inquilines and visitors than that of Teras terminalis, 
2 
