374 THE NATURAL HISTORY 



the well known spongy-oak apples springing from the 

 young shoots are the work of Cynips terminalis ; the 

 pear-shaped imbricated tumours on the roots are 

 caused by Cynips aptera, while the very remarkable 

 reddish moss-like " Bedeguar," so common on the 

 species of wild briar, results from the puncture of 

 Cynips Rosa, a fly about the twelfth of an inch long. 



The egg, when deposited in a leaf, must obviously 

 be at an inconsiderable depth below the surface at 

 first, but as it becomes gradually enveloped by the 

 morbid growth caused by the irritating fluid intro- 

 duced with it into the wound, it is eventually found 

 carried to some distance from its original position and 

 in the centre of the gall. Here, like that of the Saw- 

 fly, it increases in size for a time ; the larva, a white 

 grub destitute of feet, is shortly afterwards hatched 

 out and at once attacks the provender with which it is 

 surrounded. Some of the species undergo all their 

 transformations within the gall and only quit it as 

 perfect insects, others gnaw their way out as soon as 

 they have attained their full development as larvae, 

 and undergo their final changes in the earth. A spe- 

 cies of woody gall, showing the little round hole 

 through which the fly has made its exit, or the ir- 

 regular breach made by the Blue Tit in his search for 

 the insect before it had escaped, is very conspicuous 

 here during the winter months on the young growths 

 of the oak underwood in the covers. It is about the 

 size of the common gall nut of commerce, so useful 

 in the manufacture of ink, and is frequently found in 

 clusters of five, six, or a dozen together.* 



We now pass on to the Ichneumon Flies, under 

 which general designation we include in one group 

 the members of the four families immediately following 

 the gall-flies. Their special province is to keep within 

 due bounds the numbers of almost every other tribe 



* These are the galls of Cynips lignicola, popularly known as 

 " Marble Galls." 



