ll-i 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. tenninalis)^^ ; 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 articles ^^ 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 Cynipidas 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 

 Apliididffi 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 "^; Professor 

 Huxley ^^ made some most important researches on the life- 

 history of the Aphidid^e ; von Siebold ^° (who also is still 

 with us) and Hartig^^ (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. 



2y " On the agamic reproduction and morphology of Aphis." ' Trans. 

 Linn. Soc.,' vol. xxii., pp. 198—236, pi. 36—40 (1858). 



'^ Germar's ' Zeitschrift fiir die Entomologie,' vol. iv., pp. 379 — 381 

 (1843). 



^1 Germar's ' Zeitscln-ift fiii- die Entomologie,' vol. iii., pp. 322 — 329 

 (1842) ; vol. iv., pp. 396—400 (1843). 



