18 . THE OAK. 



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 aud 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 stored 

 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 

 stamens only are destined to wither and fall off as soon 

 as they have shed their pollen, being no longer of any 

 use. Those stalks, however, to which galls are attached, 

 remain firmly united with the tree, and grow vigorously 

 as long as the grubs contained in them continue to 

 feed. 



Another gall, resembling the last in form (being spherical), 



