112 The Galls of Essex ; a Contribution to a 



Eeaumur's 12fch Memoir^^ might be consulted with advantage, 

 and Malpighi^^ should also be referred to. 



The natural history and affinities of the gall-producers 

 come more within the field of my own entomological studies ; 

 but before entering upon that branch of my subject, I should 

 like to call attention to the "individuality," so to speak, of a 

 gall. Dr. Mayr has already recorded the fact (and I have 

 myself frequently noticed the same thing) that when such 

 galls as those of Aphilothrix radicis, Andricus terminalis, or 

 Dnjophanta folii are detached from their root, bud, or leaf, 

 and supplied with moisture, or kept on damp earth or sand, 

 they grow considerably. This is probably owing to the 

 swelling of their cells and the attenuation of the cell- walls. 

 The oak spangle galls [Neuroteri) nearly double in size, and 

 almost the whole growth of the inner larva-cell takes place 

 when the gall is on the ground, after its fall from the leaf ; 

 this must greatly alter or modify the individual cellular 

 structure. 



Two animal sub-kingdoms include species which are 

 vegetable gall makers, although these structures are mostly 

 the work of insects. Two or three species of Anguillulidae are 

 known as gall-producers ; these belong to the Annuloida. 

 Among the Arthropoda nearly all the species of the somewhat 

 abnormal but large genus Phytoptus, belonging to the Acaridea 

 (or Mites), are gall-makers, and many of them produce some 

 of our commonest plant- deformities {e. g., on the birch, lime, 

 maple, sycamore, alder, sallow, blackthorn, &c.).^* For some 

 time these were believed to be but true vegetable growths, 

 and were described as Fungi. Of the nine orders belonging 

 to the class Insecta, few contain gall-makers — Collembola, 

 Thysanura, Orthoptera, and Neuroptera being the exceptions. 



22 'Memoires pour servir a I'histoire des Insectes,' par M. de Keaumur. 

 12th Mem. 'Des Galles des plantes et des arbres.' Vol. iii., pp. 413 — 

 532; pi. 34—47 (Paris, 1737); vol. iii., pt. ii., pp. 176—333; pi. 34—47 

 (Amsterdam, 1738). 



23 ' Anatome plantarum,' Marcelli Malpighii. Part ii. ' De Gallis ' ; 

 pp. 22—50; pis. vi.— xxi., figs. 7—74 (London, 1679). 



24 See 'Economic Entomology.' By Andrew Mmray, F.L.S. Aptera, 

 pp. 331—374. (London, n. d. [1877] ). 



