i8o ANNALS OF SCOTTISH NATURAL HISTORY 



Cynipidce very generally in the centre possess a thin-walled, 

 small-celled food-mass rich in cell-contents as food for the 

 larvae. Around this is a somewhat sharply defined, more or 

 less thick, protecting layer of tissue, composed of thick- 

 walled pitted cells closely knitted together. Outside this 

 protecting layer is in most cases a comparatively thick mass 

 of thin-walled cells. In some galls this differs little from 

 the ordinary ground-tissue of the part that bears the gall. 

 In others it is, at least in part, composed of cells of very 

 irregular outline that leave wide interspaces. The epiderm 

 is as a rule not very different from that usually present on 

 the plant. On some it bears characteristic hairs, as on the 

 common Oak -spangles. The galls of other gall -makers 

 seldom show any approach to such complexity of structure. 

 In a simple closed gall there is usually only one chamber 

 occupied by the larvae ; but in some there are more than 

 one such well-defined space. Occasionally the food-mass 

 surrounded by the protecting layer forms an inner gall, 

 which separates away from the outer layers during growth, 

 the latter increasing in size more rapidly than it. In a 

 few cases, a part, like a cork in form, separates from the 

 rest of the gall, and falls to the ground, carrying the larvaj 

 with it. In some closed galls a small circular lid breaks 

 away to form an exit. Where two different forms are 

 produced by one insect (as by so many of the Cynipidtz on 

 Oaks) these usually differ much in structure as well as in 

 aspect. How great the difference may be, even when the 

 two forms are produced on the same member of the plant, 

 is well seen if one compares the soft, juicy, globular, smooth 

 currant-gall of the Oak with the firm, rather dry, lens-shaped, 

 hairy spangle, both forms growing from the leaves. 



The Compound Galls, or Bud-galls, in their more marked 

 forms appear very different from the simple forms, many 

 members of the host being frequently involved in a single 

 gall ; but it is not possible to draw a clear line of separation 

 between the two types. The compound galls are usually 

 the result of attacks on buds in a very early stage of 

 development, often before the members of the bud have 

 become recognisable as separate parts. Frequently the gall 

 is only an assemblage of parts of which each corresponds to 



