]6o Maple gall. 



diameter. But they are also found above ground where the 

 root leaves the tree. When they form a cluster around a 

 root, they give rise to a regular cylindrical swelling, which 

 may measure 5 cm. or more in diameter. This gall consists 

 at first of a firm somewhat fleshy tissue, with a small larva 

 chamber, like that of Biorhiza aptera. When mature, it 

 exhibits a wrinkled, woody, brown shell, of no great thick- 

 ness, enclosing a large cavity. 



Experim.ental breeding. The galls mature in Spring, 

 and are best collected in the month of March. They then 

 contain the perfect flies, which have wintered in them. In 

 the month of April they gnaw their way out and quit the gall. 



Fly. Length 5 mm. ; colour, ferruginous ; the face, the 

 parapsidal furrows, a line at the base of the wings, the 

 middle of the sternum, and the metathorax, blackish ; the 

 thorax slightly haired above, more strongly so at the sides ; 

 scutellum depressed, surface rugose, with a narrow smooth 

 margin ; abdomen smooth, slightly shining, the last seg- 

 ments darker above ; legs reddish brown, strongly haired ; 

 antennae with fifteen joints. 



Experimental breeding. It is comparatively easy to 

 rear this fly successfully. My own experiments were made 

 last April. I began on April 12, having prepared for the 

 purpose six small trees of Acer pseudo-platanus in pots. 

 The flies placed on the trees began at once busily to 

 examine the buds with their antennae, and prepared to 

 prick them. Their method of setting to work was rather 

 remarkable. When a fly had found a bud that suited her, 

 she placed herself in such a position, head downwards, that 

 she could drive her terebra diagonally from above towards 

 the centre of the bud-axis. She pricked the bud several 

 times, so that a number of eggs were deposited in the 

 same bud. 



I could see with the aid of a lens the openings of, the 

 little canals pierced by the terebra on the covering of the 

 bud ; and an examination of the buds which had been 

 pricked, showed that the eggs had been deposited on the 

 rudimentary leaves. According to this, the galls ought 



