18 THE OAK. 



difficulty being left untouched. You must, therefore, be 

 content to read the description of the different kinds of galls 

 which have been observed, and test its accuracy, when you 

 can, by comparing it with the natural objects themselves. 



In the first place, it appears that the different kinds of 

 insects select different parts of the tree in which to deposit 

 their eggs, and that the character of the galls produced 

 equally varies. The largest species is generally called the 

 Oak-apple, and grows on the extremity of a twig. It is 

 of a soft spongy substance, and an irregular shape, shaded 

 with brown and pink on the outside ; and it is divided on 

 the inside into a number of cells, each of which contains 

 either a small grub, a pupa, or a perfect fly, according to 

 the season. It not unfrequently happens that one of the 

 ichneumon-flies lays an egg in the body of the original 

 inhabitant of one of these cells. From this egg proceeds 

 a small worm, which lives on the substance of its pre- 

 decessor, inhabits his house, and, when grown to a perfect 

 insect, escapes, and takes flight in search of a similar 

 abode for its own progeny. What faculty, or sense, or 

 instinct can this little animal possess, which directs it to a 

 solid vegetable substance, in the centre of which is stoied 

 up proper nourishment for its young? What geometrical 

 skill enables it to discover in what part of the mass its 

 prey lies buried? By the aid of what calculating power 

 does it contrive to pierce the body of the included grub 

 only so deep as to deposit its egg in a place of security, 

 without wounding any vital part? The most remarkable 

 kind of Oak-gall, next to that described, is produced by 

 another insect of the same genus (Cynips). This fly 

 deposits its eggs in the stalk of the stamen-bearing flowers, 

 which is long and drooping. The excrescence which 

 follows resembles a currant in size, shape, and even in 

 mode of growth, it often happening that several are placed 

 at short distances from each other on the same thread-like 

 stem. There is a remarkable fact connected with this 

 species of gall. Those flowers of the Oak which bear 



