1 86 ANNALS OF SCOTTISH NATURAL HISTORY 



between the parts of the buds, which may be considerably 

 enlarged. Occasionally (e.g. on the Bedstraws) the bud- 

 galls may be conjoined to form pretty large masses. The 

 larvae of some gall-midges pupate in the galls, while others 

 leave the galls to pupate in the soil. 



The Trypetidtc, a family of flies with spotted wings, and 

 often not unlike the common house-flies in form and size, 

 afford a small proportion of gall-makers, especially affect- 

 ing Composites. On these plants the galls are formed either on 

 the stem (Urophora Cardui on thistles), or in the flower- 

 heads (Trypeta solstitialis or Centaurea nigrd}. 



LEPIDOPTERO-CECIDIA are few, and of no special in- 

 terest. They consist almost exclusively of thickenings of 

 leaf-stalks, leaf-veins, or stems. 



HVMENOPTERO-CECIDIA are numerous and varied, but 

 all belong to the closed type, usually of simple galls, though 

 bud -galls are not uncommon. The gall-makers in this 

 division fall under the families Tenthredinidce or Saw-flies, 

 Chalcididce, and Cynipidce or true Gall-flies. All Hymen- 

 optero-cecidia belong to the closed type, the mother, by means 

 of the ovipositor, making a wound in the tissues, in which 

 she deposits an egg. Afterwards the wound heals up. 

 The Saw-flies make swellings in the twigs or leaf-stalks, 

 or produce more conspicuous galls on leaf-blades, especially 

 on Salix. These leaf-galls are pea-shaped and affixed by 

 a narrow support ; or they are bean-shaped and sunk, singly 

 and in pairs, in the leaf, projecting on both surfaces. The 

 galls are fleshy, and are composed chiefly of cellular tissues, 

 the inner tissue forming a food-mass which is eaten away 

 by the larva. There is no well-defined larval chamber ; 

 nor do the walls of the gall show clearly defined layers of 

 tissue. 



The Clialcidid(Z are mostly parasites on other insects, or 

 dwellers in galls of true gall-makers, but the genus Isosoma 



o o o 



causes thickenings on the stems of grasses, sometimes 

 covered over with short broad leaf-sheaths, as on Couch- 

 grass. The galls of the Cynipidcs have been so frequently 

 referred to in the course of this paper as to make any 

 lengthy reference to them here out of place. They show 

 frequently the greatest degree of complexity in structure 



