PROCEEDINGS OF THE PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
123 
coloured maggot existing in the centre of each. It maybe 
that some may go farther in their desire for knowledge, 
and may collect some of the galls, particularly of the hard 
woody forms, and, putting them into some secure recep¬ 
tacle, may allow them to remain in it till the following 
spring, occasionally glancing at them to see what results 
from them. After a time, in most cases, there will be 
found along with the galls some small four-winged flies, 
belonging to the Hymenoptera; but though naturally we 
might be inclined to suppose that these are the makers of 
the galls, it will be remembered from what has been said 
above, that this conclusion may be erroneous. Besides 
the gall-makers the observer will often find among the 
insects that emerge from the gall allied Cynipkte, some of 
which are simply guests reared from eggs of species that 
do not form galls for themselves, but only lay their eggs 
in the galls made by the true gall-flies. Other species 
may belong to a group of Cynipidte that have developed 
the habit of parasitism, not being mere guests as in the 
former cases, where the guests may indeed destroy the 
legitimate occupant of the gall by eating all the food that 
ought to be available for its nourishment, but do not wil¬ 
fully injure the true owner. The parasitic species, pro¬ 
perly so-called, on the contrary, destroy the gall-maker, 
as thelatter isthe food on which theparasiticlarvalives. But 
besides these Cynipideous guests (inquilines) and para¬ 
sites, there may be numerous insects of other groups 
reared from the galls; and among these are to be found 
both guests and parasites, no less than among the species 
more nearly related to the gall-makers. Many of these 
other insects are small Hymenoptera, belonging to groups 
(Encyrtidce, Torymida, Chalcididce ), that have a consider¬ 
able resemblance to the Cynipid*, though others are more 
widely different in their aspect, some of the latter even 
belonging to the smaller moths or to beetles. Indeed, a list 
of the insects that have been reared from, for example, the 
large round marle-like galls of Cynips Kollari Hart (the 
“Devonshire gall”), now so widely spread in Scotland, 
would certainly much surprise even an entomologist, if he 
had not previously directed any attention to these bodies 
and their occupants. It will be understood from what has 
been said that the determination of the gall-makers is not 
so easy a task as might at first be imagined, and as might 
be believed from the ease with which insects can be reared 
from many of the oak-galls. The identification of the 
insects when reared can be effected with certainty only by 
a special adept, inasmuch as the general similarity between 
undoubtedly distinct species of Cynipidse is extremely 
close in many cases, while frequently the different broods 
of a dimorphic species are more unlike one another than 
they are to allied species. Mr Cameron stands pre¬ 
eminent in Scotland, I may say in Britain, in this diffi¬ 
cult task; and to his labours do we owe much of our 
recently-acquired knowledge of Scottish Cynipid® and 
their galls. 
On referring to the older writings that treat of galls, 
such as Reaumur’s and De Geer’s works, we find that oak- 
galls occupy a very prominent place among the forms 
spoken of. Many of the figures and descriptions in these 
works are exceedingly good, and show a keen power of 
observation; but naturally the knowledge of the writers as 
to the origin of the galls was somewhat uncertain. In 
some of the older works the ideas suggested as to their 
origin, and as to the mode in which the larvae usually 
found in them (on cross section) gained admission to their 
interior without leaving any external mark of the passage 
through the tissues of the gall, are often very amusing in 
what we now regard as their absurdity. However, it is 
needful for us to remember that we are still in little less 
darkness than our predecessors as regards many of the 
most common and necessary functions of life, and that 
many of the so-called explanations at present in vogue will 
probably seem to our successors as absurd as anything to 
be found in the works of those to whom, with all their 
errors, we owe the possibility of the great advances that 
have been made since they lived and laboured in the mists 
of perplexity, with little to aid them in their efforts to 
reach the truth. Small though their progress may often 
seem, it was great if measured by their opportunities and 
means of investigation, and they rendered the attainment of 
truth possible by clearing away the mass of error that had 
so greatly prevented their own advance. 
Among the different forms of oak-galls that must be 
familiar to almost all my hearers are several that I may 
recall to recollection in a few words devoted to each. 
Galls on oaks, the work of true gall-flies, are found on all 
parts of the tree, from the roots to the parts of the flower, 
each kind usually being restricted to some one set of organs 
of the tree; for example, the lenticular rusty brown “ oak- 
spangles” are seldom, if ever, met with on any part but the 
leaves, though so common that there are very few leaves 
on which one or two may not be found in most places in 
the month of September; and many leaves are so loaded 
with them on the lower surface, to which they are con¬ 
fined, that hardly a spot the size of a pin’s head is left free 
from them. Many galls in like manner are exclusively 
confined to the buds, such as the “ Artichoke gall,” which 
derives its name from its great likeness to a small arti¬ 
choke. A comparatively small number of galls may be 
found on more than one organ of the plant. As an ex- 
