PROCEEDINGS OP THE PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
121 
interest to attract their study. However, in this, as in 
most scientific pursuits, familiarity does not lessen the 
pleasure and interest to be derived from the study; and 
the explanation of the perplexing mysteries has only added 
to the inducements already existing to take up the investi¬ 
gation of those creatures. It may almost be said that year 
by year the phenomena of “ dimorphism,” in one or other 
of its various forms, are found to be more and more widely 
spread among the lower groups of animals ; but among in¬ 
sects it has been known in comparatively few cases, the 
Aphides being the best group to exemplify it till within 
late years. It may be said to consist essentially in thisi 
that there are in the full life-history of any species in 
which it occurs two forms of the insect, or, as it is at times 
expressed, two generations, of which the one possesses 
both males and females and produces offspring in 
the usual way, while the other consists of so-called females 
alone, and reproduction is effected by what we may regard 
as a process of budding from a part of the body of the 
parent, not by the true sexual method. This latter genera¬ 
tion is really asexual, not (in function) female at all, 
though frequently it resembles exceedingly the ordinary 
female in appearance ; and the eggs produced by them are 
indistinguishable in appearance from ordinary eggs sexu¬ 
ally fertilised and developed in the ordinary way. In 
many cases the asexual generation produces living young 
ones, as in many or indeed most of the Aphides, by the 
process of budding above alluded to. It is, however, 
practically impossible to draw the line between the asexual 
and the sexual methods of reproduction, inasmuch as there 
are not a few cases known in which true females, if not 
fertilised in the usual way, are capable of laying eggs that 
will go on to develope in the usual course, and will produce 
healthy offspring. Numerous examples of this have oc¬ 
curred among the Lepidoptera ; but perhaps its occurrence 
is more widely known among the Honey or Hive Bees, in 
which the unimpregnated eggs give rise to male or drone 
bees, while the impregnated eggs of the same female pro¬ 
duce larvae capable of being developed into neuters or into 
queens, according to the accommodation allowed them in 
the cell, and to the kind and amount of food given them. 
Among the Gallmakers this dimorphism or alternation of 
generations is met with in the groups known as the Gall¬ 
flies or Cynipidae and the Green-flies or Aphides. 
Let us commence, then, with the Cynipidae. These 
insects are not, on the whole, a very numerous group; and 
in Scotland, so far as I am -aware, their galls have been 
found on plants belonging to only the genera Quercus, 
Rosa, Hieracium, Potentilla, Rubus, Nepeta, and (?) 
Triticum; but in other countries they form galls on plants 
of a good many genera besides these. Of all the genera 
mentioned, one stands out pre-eminently as gall-bearing, 
the Oaks ( Quercus) supporting more than half the galls 
known to be the work of Cynipidae. Next in frequency 
to the Oaks, in number of the kinds of galls they bear, 
but very far behind in numbers, come the Hoses. The 
remaining genera do not, as a rule, bear more than one or 
two kinds of galls of this group of insects. Those desirous 
of obtaining a wide knowledge of the galls of Cynipidae 
will find that there have been not a few works devoted to 
their elucidation, either to them exclusively, or to them 
along with the galls of other groups of insects. Among 
the most valuable of these special works may be noted the 
following;— Die mitteleuropceischen Eichengallen; Europce- 
ischen Cynipidengallen, and other very excellent papers by 
Dr Gustav Mayr, of Vienna; Dr Adler’s now well-known 
paper on the Dimorphism of the 0% nip idea, either in the 
original German or in the translation into French by M. 
J. Lichtenstein; Hartig’s Ueber die Familial der Qall- 
wesptn; Beyerinck’s Die ersten Entwickelungsphasen 
einiger Cynipidengallen ; various papers by Mr Peter 
Cameron, of Glasgow, in the Etomologist’s Monthly Maga¬ 
zine and in The Scottish Naturalist, some articles by my¬ 
self in the same magazines; and several articles by Walsh, 
Bassett, Fitch, and other American entomologists. But 
even an enumeration of the papers that would require to 
be consulted to gain a thorough knowledge of the life- 
history and of the systematic arrangement of the Cynipidae 
would only be tedious at this time, nor could such an 
enumeration serve any good object here. 
It may be not amiss to note in passing that the Cyni¬ 
pidae, though all belonging to the group popularly and par 
excellence known as Gall-flies, are not by any means uni¬ 
versally makers of galls. Many of them are inquilines, 
i.e., they live as (unwelcome) guests in the galls formed 
by the gall-making species; hence in rearing the insects 
from the galls, it is necessary to exercise not a little cau¬ 
tion in regarding all and sundry Cynipidae that emerge 
from them as being gall-makers. We should soon have 
far more than “ dimorphism” among them if led astray by 
any such error of observation. It may be that these 
inquilines are descendants of true gall-making species, 
which have found it more easy for themselves to take 
advantage dishonestly of their kinsfolk’s labours to pro¬ 
vide themselves with food and shelter, as is indeed ex¬ 
emplified not seldom in the higher animal—man. They 
are often closely allied to gall-making species. Other 
Cynipidae have taken to still less creditable modes of 
gaining a living, and have become degraded into the con¬ 
dition of true parasites, like the Ichneumon flies in {hat 
