13) 
PROCEEDINGS OF THE PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
Asexual. Emerge. Sixes distinct. Emerge. 
Biorhiza aptera Winter. Dryoteras terminalis July. 
„ renum ,, Trigonaspis megaptera June. 
FORMS OF WHICH THE RELATIONS HAVE NOT YET BEEN 
DETERMINED. 
(a) Asexual. 
Aphilothrix solitaria. 
„ Clementinae. 
,, callidoma. 
„ albopunctata. 
Cynips Kollari. 
Andrieus quadrilineatus. 
(Ia most of these the galls are found in spring, but the insects 
emerge in late autumn or in the following spring.) 
(b) Sexes distinct. 
Andrieus amenti. 
,, aestivalis. 
(These are found on the male catkins, hence both are formed in 
summer, and both are probably dimorphic.) 
The table just given shows at a glance that in no case do 
the two forms now referred to the same species belong to 
the same genus under the classification formerly employed. 
For example, if we take Spathegaster baccarum, forming 
the “ currant galls,” we shall find it produce the “ oak 
spangles,” referred to Neuroterus lenticularis. The insects 
produced from the two forms of galls differ very con¬ 
siderably from one another in structural characters, em¬ 
ploying those afforded by the parts about the ovipositor 
for generic distinctions; so that they are more similar in 
appearance to allied but truly distinct species than they 
are to one another. 
A still more marked example of great differences be¬ 
tween the two generations of the same species is seen if 
we compare Trigonaspis megaptera, reared from the pea¬ 
sized galls on the trunks of oaks, with Biorhiza renum, 
reared from the small kidney-shaped galls on the leaf- 
veins; yet experiment has shown the genetic relationship 
of the two. T. megaptera possesses large wings, while B. 
renum. is wingless; the legs are relatively much longer in 
the former; the form of the body is very different in the 
two, as is also the colour; and the antennae are much longer 
in the former. T. megaptera shews both sexes; B. renum 
possesses no males. 
To understand the existence of such differences, it is 
needful for us to bear in mind that the insects in the two 
generations find the parts of the plant on which they have 
to operate to deposit their eggs so different in accessibility 
and in texture, that the instrument suited for the purpose 
ia the one, would fail altogether under the conditions in 
which it is required by the other. As an example is more 
easy to follow than the abstract grounds for an assertion, let 
us look at the conditions for Spathegaster baccarum and Neu¬ 
roterus lenticularis. For convenience of reference, they will 
be referred to as if they were quite distinct species. The 
former emerges in June, and produces galls on the backs 
of the leaves after these are fully unfolded; hence it does 
not require a long ovipositor to reach the proper situation 
for the egg, and, therefore, for the gall. Its ovipositor is 
found to be straight for the greater part of its length, and 
not so long as the abdomen. In N. lenticularis, on the 
contrary, the ovipositor requires to be long, as the insect 
has to bore in between the scales of the still closed bud, in 
order to deposit its eggs in the young leaves. This long 
ovipositor is accordingly found to exist, and to gain the 
necessary protection it is rolled up so as to be packed away 
safely between the plates of the abdomen. To allow of its 
protrusion the hard parts and the muscles alike require to 
be considerably modified as compared with those of the 
straight short ovipositor of the Spathegaster. 
Analogous needs exist, met in the same way, if we com¬ 
pare Trigonaspis megaptera, which deposits its eggs in the 
surface of leaf veins of the opened leaves, with Biorhiza 
renum, which has to push its ovipositor into the closed 
bud, there to deposit its egg in the growing-point of the 
bud. It may be observed, though not bearing on the sub¬ 
ject immediately under consideration, that the formation 
of the gall has been found not to begin till the larva 
emerges from the egg, and that the death of the larva at 
an early period is usually followed by the mal-develop- 
ment of the gall. 
Time will not allow of entering farther, at present, upon 
the various interesting questions that present themselves 
in this new field of biological study; nor will it allow me 
to do so as I had proposed to myself, viz., to give a resume 
of the dimorphism that has been found to exist in the 
group of gad-making Aphides. This is, however, the less 
to be regretted that they form only a very small group of 
gall-makers in Scotland; and very little has been done in 
working out their occurrence here. M. Lichtenstein has 
during the past few years been conducting very painstak¬ 
ing researches on these insects in France, and has pub¬ 
lished several articles on them in the Entomologist’s 
Monthly Magazine. 
I shall conclude this paper with a list of the Cynipid® 
of which the galls have been recorded from Perthshire, 
in the hope that it may stimulate members of the Society 
to a search after the forms recorded from other parts of 
Scotland, but not yet detected in Perthshire. The galls 
