114 The Galls of Essex; a Contribution to a
necessary it is to keep each species of gall separate, as it will
greatly assist him in his studies until he is conversant with
the gall-makers, their inquilines and parasites. How large
is the subject will be seen when I mention that the late
Francis Walker bred 54 species of insects from the well-
known "oak-apple" (gall of A. terminalis)26; and so with our
now commonest oak-gall—the Devonshire or marble gall of
Cynips Kollari. Up to 1872 but two extra lodgers other than
the legitimate inhabitants of this gall were known. In two
recent articles27 I have been able to identify 75 Hymenoptera,
12 Lepidoptera, 13 Coleoptera, 1 Orthopteron, and 2 Neurop-
tera, in all 103 species ; the whole bred from the small world
of a C. Kollari gall, and still I believe these various tenancies
are far from exhausted.
The cycle of life in the gall-making Cynipidae forms a sub-
ject of the greatest biological interest. The older authors were
generally astonished, and expressed their inability to find a
satisfactory explanation ; and it was not until some fifty years
since that the various methods of reproduction received that
scientific treatment which they deserved. The Cynipidae and
Aphididae amongst the hexapods divided the interest in being
the highest exponents of the various processes of non-sexual
reproduction. Professor Owen, who is still amongst us, was
the first to employ the term "parthenogenesis "28; Professor
Huxley29 made some most important researches on the life-
history of the Aphididae ; von Siebold30 (who also is still
with us) and Hartig31 (who went over to the majority but
last year) on the Cynipidae. The theories of non-sexual
26 'Zoologist' iv., p. 1454 (1846).
27 'Entomologist' xii. 113 (May, 1879); xiii. 252 (November, 1880).
28 'On Parthenogenesis, or the successive production of procreating indi-
viduals from a single ovum.' London, 1849. Consult Felix Plateau's
'Etudes sur la Parthenogenese,' Gand. 1868.
29 "On the agamic reproduction and morphology of Aphis." 'Trans.
Linn. Soc.,' vol. xxii., pp. 193—236, pl. 36—40 (1858).
30 Germar's 'Zeitschrift fur die Entomologie,' vol. iv., pp. 379—381
(1843).
31 Germar's 'Zeitschrift fur die Entomologie,' vol. iii., pp. 322—329
(1842); vol. iv., pp. 396—400 (1843).