276 THE ENTOMOLOGIST. 



The leaves are examples of the first class of organs ; the 

 acorns of the last. The gall-makers exercise a direct inter- 

 ference with this natural propensity : they set up a local 

 inflammation or irritation in the constitution of the oak, in 

 order to compel it to elaborate a certain description of food 

 adapted to the requirements of their young; the ordinary 

 productions of the oaks, in their normal or natural state, not 

 being adapted to this purpose. Here, then, are two antago- 

 nistic forces : the oak struggling to preserve itself and its 

 kind; the gall-maker compelUng it to produce something 

 quite different, namely, food suited to preserve itself and Us 

 kind; the struggle is never ended. The oak is required, 

 whether by the diversion of its sap into new channels, or by 

 a certain chemical change in the character of its sap caused 

 by the injection of a new element, — this is still a moot 

 question, — to elaborate new substances : it does not willingly 

 comply ; and although unable to resist the requisition, 

 although unable to say, "I will not produce a nasty, fungoid, 

 spongy substance for food of the infant gall-makers," it does 

 so with as bad a grace as possible ; it seems to say, " If T 

 must, I must, but I do it very reluctantly, and will make your 

 new diseased food as much like the old healthy food as 1 

 possibly can." So the gall-maker strives to produce deformity 

 and abnormality, and the oak all it can to maintain uniformity, 

 normality, good order, and legitimate produce : the result is 

 the production of spongy food for the Cynips in the familiar 

 form of acorns, or rather caricatures of acorns, so grotesque 

 that we can scarcely recognize them. 



Let us enquire how this struggle — this contention between 

 the giant oak and the pigmy Cynips — is carried on. Let us 

 examine Dr. Mayr's beautiful work, 'Mitteleuropaischen 

 Eichengallen,' and ascertain what evidence it affords of the 

 value of my theory. Dr. Mayr has described and figured 

 ninety-six species of oak-galls, many of which have been 

 found in Britain. His figure 5 represents the gall produced 

 by Aphilothrix Sieboldii ; the little acorn-like objects, more 

 than fifty in number, represented as forcing their way through 

 the rind of the twig, have assumed the form of the very 

 young acorns of Quercus sessiliflora ; each consists principally 

 of an involucre or cupule, the undivided style projecting in 

 the centre : this is very conspicuous and strongly pronounced ; 



