List of the Insect Fauna of the County. 111
in natural history. And I am sure, from all I know of
naturalists, that they will gladly let any of you into their
fields, though you may use them for your own purposes much
more than for theirs. It would be difficult to find a field for
the study of the very principles of pathology larger or richer
than this offers to you. The objects are within easy reach ;
hundreds of morbid processes are at hand for deliberate study;
experiments may be made at will; during many months,
thousands of insects, as natural vivisectors, will be at work
for you, and it must yet be some years before they will be
required to take out licences." [Op. cit., pp. 20—28].
With these pregnant suggestions, I now leave the origin
and growth of galls, and pass on to the insects which produce
them; but once again expressing the opinion that mechanical
irritation rather than the action of a specific virus is the pro-
bable explanation of gall-growth.
The vegetable-structure of the various galls deserves a
separate memoir, and I leave this in the hands of some of
our botanical members, contenting myself with referring
them to the following important articles by Meyen,16 Lacaze-
Duthiers,17 Prillieux,18 Beyerinck,19 Courchet,20 and Frank.21
16 Meyen, 'Pflanzen-pathologie' (1841), divided into:—'Ausclrwellungen,'
Odemata, pp. 63—65; 'Blasenformige Auftreibungen,' Emphymata,
pp. 65—66; 'Fleischgewachse,' Sarcomata, pp. 66—68; 'Gallapfel,'
Gallae (on oaks chiefly), pp. 68—71. There is also a French version,
'Traite de Pathologie Vegetale.' I have not been able to find the works
either in the libraries at British Museum, Kew, or the Linnean Society.
17 'Recherches pour servir a l'histoire des Gralles,' par M. Laeaze-
Duthiers. 'Annales des Sciences naturelles,' Botanique, 3rd Series, vol.
xix., pp. 273—354 ; pl. 16—19 (Paris, 1853).
18 'Etudes sur la formation et le developpement de quelques Galles,'
par M. Ed. Prillieux. 'Annales des Sciences naturelles,' Botanique, 6th
Series, vol. iii., pp. 113—137; pl. 16—18 (Paris, 1876).
19 ' Bijdrage tot de Morphologie der Plantengallen.' By M. W. Beijer-
inck. 92 pp. and 2 plates (Utrecht, 1877).
20 ' Etude sur les Galles causees par des Aphidiens,' par M. L. Courchet.
'Academie des Sciences et Lettres de Montpellier ; Memoires de la section
des Sciences,' vol. x., pp. 1—102; pl. i.—vi. (Montpellier, 1881).
21 Frank's 'Me Krankheiten der Pflanzen.' Breslau, 1881. For galls,
see pp. 661—798.