Marvels of the Universe 1051 
oviposit usually in {the more tender rootlets. As a result, another kind of gall is formed—this 
time an outgrowth from the root. At first it is soft, while it may be pink or reddish in colour ; 
but it soon becomes hard and nut-like. These root-galls are typically unicellular—z.e., each con- 
tains only one larval chamber ; but they are often crowded closely together in masses which look 
like one large gall. As in the case of the Oak-apple, the grubs change to pupe in the galls, and 
during the winter and early spring the perfect insects emerge—these, of course, being the wingless 
females with which our life-history commenced. To recapitulate: Oak-apples are abnormal pro- 
ductions of the oak-tree, due to the activities of a small insect which lays its eggs in the buds. 
They give rise to a summer brood of “ flies,’ comprising males and females, which differ in 
many ways from the parent form. The females lay their eggs in the root of the oak, and thus 
induce the formation of another kind of gall, from which in due season the winter generation 
of the species emerges—this 
generation consiSting of wing- 
less females, capable of virgin 
reproduction, which complete 
the cycle by laying their eggs 
in oak-buds. 
Thus this wonderful alter- 
nation of generation—this in- 
terchange of personality, as it 
were—goes on year after year ; 
and in this way we get our 
Oak-apples. These facts were 
not known to the old natural- 
ists, who gave the insect which 
emerged from each kind of gall 
a different name. Thus, while 
the generation which is bred 
in the root-galls was appro- 
priately dubbed apftera (i.e., 
without wings), their offspring 
were termed teyminalis—because 
the Oak-apple commonly arises Photo by] a TT Rb Baa 
from a terminal bud. In order SSS OF GALL WATS 
g ‘ A section through a terminal bud of an oak-twig, showing the eggs laid by the 
to avoid confusion, these names —«\inter female.” Their presence so acts upon the bud that instead of developing 
are still retained by writers ; into a shoot it swells into the familiar Oak-apple. 
they do not, however, stand for distinct species, but for two recurrent forms of one and the same 
insect. 
In the foregoing paragraphs the writer has employed the word “ fly ”’ to describe these wonderful 
gall-insects because the term is in common use. We must remember, however, that it is really a 
misnomer. Strictly speaking, a fly—e.g., the blue-bottle or the daddy-longlegs—has only one 
pair of wings ; whereas these gall-insects have two pairs of wings, like wasps and bees, to which, in 
fact, they are not distantly related. Thus they are more fittingly referred to as gall-wasps. 
A very large number of insects live at the expense of the Oak-apple, or of the gall-wasps to which 
it rightly belongs. Some of these are parasites which devour the larve or pupe. Others are so- 
called inquilines, or guest insects. The latter are nearly related to the true gall-wasps, but instead 
of forming galls on their own account the parent insects insert their eggs into existing galls. Thus, 
the mere fact that an insect emerges from an Oak-apple is no proof that its parent was the originator 
of the gall. Oak-apples are also burrowed into and eaten by the grubs of beetles, the caterpillars 
