GROWTH OF THE GALLS. 405 



forced into an abnormal growth, and rapidly encloses the egg. 

 Sometimes, especially on leaves, the galls are quite spherical, 

 and of about the same consistence as a green gooseberry. Other 

 leaf-galls are quite flat, like so many small coins stuck on the 

 leaf; while others hang by strings like bunches of currants. 

 Some are covered with leaf-like appendages, and look like 

 miniature artichokes ; while others, like the well-known bede- 

 guar of the rose, are clothed with a dense mass of long, soft 

 filaments. 



In the midst of the gall lies the young larva, which feeds 

 upon the soft centre of the gall, and by continually eating 

 makes for itself a little cell, which increases in proportion to the 

 size of its body. It is evident that all locomotion is denied to 

 the larva, and that all it can do is to turn round and round in 

 its cell. Consequently it has no legs, and is only able to move 

 itself about by the edges of the rings or segments of its body. 



As a general rule, the larva remains in the gall until it 

 assumes the perfect form, and then gnaws its way into the open 

 air. There are some species, however, which wriggle their way 

 out of the gall before they become pupse, fall to the ground, 

 burrow in it, and there undergo their changes. Generally there 

 is only one larva in each gall, but there are several species in 

 which a great number are found in the same gall, each larva 

 occupying its separate cell. The bedeguar of the rose and the 

 oak-root gall are familiar British examples of these compound 

 galls. 



Even in England there are many species of Gall Flies, while 

 the foreign species seem to be without number. In the collec- 

 tion of the British Museum, besides a vast number of species 

 that have been named, described, and arranged, there are whole 

 drawers full of species that have as yet received no name. They 

 are all little insects, the species which is drawn on page 405 

 being one of the largest. The figure is magnified two and a half 

 diameters. It is one of the American insects, the specimen 

 which is figured having been taken in Massachusetts. As is 

 the case with most of the genus, the colour is dark, being 

 simply shining black. The wings are translucent, with the 

 exception of the spot, which is black, fading into brown. 



These insects are examples of the uses that lie hidden in 

 Nature. Many thousands of years had the Gall Flies been making 



