618 THE MICROSCOPE. 



four plates are seen to enter into their construction: 

 namely, two saws, placed side by side, as in fig. 277 ; 

 and two supports, somewhat like the saws in shape. A 

 deep groove runs along the thicker edge of the latter, 

 which is so arranged that the saws glide backwards and 

 forwards, without a possibility of running out of the 

 groove. When the cut is made, the four are drawn 

 together; and through a central canal, which is now 

 formed by combining the whole, an egg is protruded 

 into the fissure made by the saws in the leaf. The cutting 

 edges of the saws are provided with about eighteen or 

 twenty teeth : those have sharp points of extreme delicacy, 

 and together make a serrated edge of the exact form 

 given to the finest and best-made surgical saws. In the 

 summer-time the proceedings of this little insect can bo 

 watched, and the method of using this curious instrument 

 seen, by the aid of a hand magnifier ; they are not easily 

 alarmed when busy at their work. 



Many other insects are provided with instruments for 

 boring into the bark or solid wood itself. The Cynip bores 

 a hole into the side of the oak-apple, 

 for the purpose of depositing her egg. 

 The larva when hatched finds a com- 

 fortable lodging, and a good supply of 

 food ; when full grown, it eats its way 

 out of the nut, and, dropping to the 

 ground, it assumes the form of the per 

 feet fly. The most important of this 

 family is the Cynip gallce tinctorive, 

 . 278, which is the cause of the gall- 

 Gall-fly and larva. nu ^ a nut most extensively employed 

 in the manufacture of ink and for dyeing purposes. 



Some of the Wasp tribe, so very peculiar in their habits, 

 are active agents in the economy of nature. The solitary 

 Mason-wasps curiously construct nests in the form- of 

 cells, for the purpose of carefully rearing their young. 

 The social-wasps, like bees, live in communities, and 

 have nearly the same divisions of labour and regulations 

 for the good government of the colony. The struc- 

 ture and mechanical contrivance of the wasp's sting can 

 only be seen under the microscope. The sting consists of 



