340 INSECT ARCHITECTURE. 



woody galls on various plants, such as the tliistle-fly 

 (Tephritis cardui, Late.). Tlie grubs of this pretty fly 

 produce on the leaf-stalks of thistles an oblong woody knob. 

 On the common white briony (^Bryonia dioicct) of our hedges 

 may be found a very pretty fly of this genus, of a yellowish- 

 brown colour, with pellucid wings, waved much like those 

 of the thistle-fly with yellowish brown. This ^j lays its 

 eggs near a joint of the stem, and the grubs live upon its 

 substance. The joint swells out into an oval form, furrowed 

 in several places, and the fly is subsequently disclosed. In 

 its perfect state, it feeds on the blossom of the briony. 

 (J. E.) Flies of another minute family, the gall-gnats 

 {Cecidomyice, Latr.), pass the first stage of their existence 

 in the small globular cottony galls which abound on ger- 

 mander speedwell ( Veronica chamoedrys), wild thyme (Thymus 

 serpyUurn), and ground-ivy (^Glechoma hederacea). The latter 

 is by no means uncommon, and may be readily recognised. 

 Certain species of plant-lice (Aphides), whose complete 

 history would require a volume, produce excrescences upon 

 plants which may with some propriety be termed galls, or 

 semi-galls. Some -of these are without any apertuie, whilst 



A Plant-Louse (.l^j/i?*), magnified. 



others are in form of an inflated vesicle, with a narrow 

 opening on the under side of a leaf, and expanding (for the 

 most part irregularly) into a rounded knob on its upper 

 surface. The mountain-ash (Pyrus aucuparid) has its leaves 

 and young shoots frequently affected in this way, and 

 sometimes exhibits galls larger than a walnut or even than 

 a man's fist; at other times they do not grow larger than a 

 filbert. Upon opening one of these, they are found to be 

 filled with the aphides sorhi. If taken at an early stage of 



