ERIOPHYID^E OR GALL-MITES. 27 



Species living in Galls. 



There are numerous species living in galls on the leaves of various 

 trees, but the following are a few typical examples. They are not 

 true galls, however, but simply pseudo-galls ; and it is important to 

 compare the structure of the pseudo-galls of Eriophyinae with the true 

 galls of gall-forming insects. The former is simply an abnormal thick- 

 ening of the leaf, with an opening or passage leading into the pseudo- 

 gall. The opening is surrounded by hairs, which doubtless act as a 

 protection against the inroads of parasitic acari and other natural 

 enemies. The true gall, on the other hand, is always closed, and the 

 form variable and immaterial. Some species of leaf-miners (Lepidop- 

 tera) form conical galls or cases on the upper side of the leaf, but the 

 passage communicates between the epidermal skins, and has no open- 

 ing through the under side of the leaf, as in the gall of Eriophyinae. 



Eriophyes tili.e (typicus) (Xal.) 



In fig. 26 we have represented what are popularly known as " nail- 

 galls " on the leaves of the lime-tree Tilia europcea. This is a very 

 interesting species, inasmuch as nail-galls 

 were first considered by Eeaumur, the 

 celebrated French entomologist, to be a 

 special vegetable formation accruing from 

 the action of animal life ; but in the 

 absence of any description it is doubtful 

 whether he saw the real tenant, or simply 

 a parasitic lodger. 



Mr Andrew Murray remarks : "Whether 

 Eeaumur saw them or not, at least no one 

 else did for about 100 years after. About 



" Fie. 26. " Aatl-galls on leaf of 



1832 and 1834, however, the publication "me tree (Tilia leuropaea) caused 



r by Eriophyes tiliae. 



of M. Duges' valuable papers on the 



classification of the Acaridae, to which we have already had so often 

 to refer, gave an impulse to their study, which led to fresh dis- 

 coveries ; and M. Turpin observed in the nail-galls of the lime leaf a 

 quantity of very minute, semi-transparent, fleshy mites, of a new and 

 hitherto unknown form, a narrow creature with two pairs of small 

 legs at its head, and some kind of sucker apparatus at its tail, on 



