XIV INTRODUCTION 



variety of forms on numerous plants. One form is 

 illustrated on Plate LXIII, and others are referred to 

 elsewhere. 



Of the Cynipidas there are many species. They 

 attack various plants, but they are found principally 

 on the oak. They have four wings, and to distinguish 

 them from other gall producers may correctly be 

 known as gall- wasps, and henceforth they will be 

 referred to as such. They are briefly described in 

 Chapter IV. 



While the Diptera are comparatively free from the 

 attacks of other insects, the gall-wasps are not ; they 

 are extensively preyed upon by parasites, and hyper- 

 parasites, and the gall tissue around the larva is often 

 the welcome abode of a host of other creatures which 

 play the parts of inquilines, commensal tenants, or 

 casual occupants. They seldom cause the death of 

 the rightful inhabitant except in the case of inquilines 

 living gregariously around the larval cell of Cynij^s 

 Kollari. The number of lodgers in oak galls is very 

 great (more than 180), a good many occurring in 

 several kinds of galls. Eurytoma rosse occurs in four- 

 teen different galls, Megastigmus doisali.s in eleven. 

 Synergy s facialis in ten, S. vulgaris in nine, and five 

 other parasites each in eight galls. There are many 

 more of similar habits. 



It will be found that thirteen species are without 

 alternate generations, viz. : Andricus sestivaJis, = 

 amenti, ■=: clementinse, = glandium, = glandulai, = 

 h(cidus, = solitarius, Apliilothvix alb ojmn data, = 

 viarginalis, = quadrilineafns, = seminationis, Dryo- 

 phanta agama, and = disticha. At present these are 

 unknown ; and of two other species there is yet some 

 doubt. In this, however, our British species are not 

 alone. According to Beyerinck the sexual generations 

 of twenty-six continental forms are unknown (p. 152). 



A very large numljer of oak galls occur in Mid- 

 European countries. The various species and varieties 

 of oak are also numerous, consequently a great many 



