160 EVEX1XGS AT THE MICROSCOPE 



twenty-four. The grooves are usually placed in a line, at 

 a small distance from one another, on the same branch; 

 but sometimes the mother- fly shifts to another, or to a 

 different part of the branch, when she is either scared or 

 finds it unsuitable. She commonly, also, takes more than 

 one day to the work, notwithstanding the superiority of her 

 tools. Keaumur has seen a Saw-fly make six grooves in 

 succession, which occupied her about ten hours and a half. 



"The grooves, when finished, have externally little 

 elevation above the level of the bark, appearing like the 

 puncture of a lancet in the human skin; but in the course 

 of a day or two the part becomes first brown and then 

 black, while it also becomes more and more elevated. 

 This increased elevation is not owing to the growth of the 

 bark, the fibres of which, indeed, have been destroyed by 

 the ovipositor- saw, but to the actual growth of the egg; 

 for, when a new-laid egg of the Saw-fly is compared with 

 one which has been several days enclosed in the groove, 

 the latter will be found to be very considerably larger. 

 This growth of the egg is contrary to the analogy observ- 

 able in the eggs of birds, and even of most other insects; 

 but it has its advantages. As it continues to increase, it 

 raises the bark more and more, and consequently widens, 

 at the same time, the slit at the entrance, so that, when 

 the grub is hatched, it finds a passage ready for its exit. 

 The mother- fly seems to be aware of this growth of her 

 eggs, for she takes care to deposit them at such distance 

 as may prevent their disturbing one another by their de- 

 velopment. ' ' * 



The merry little jumping insects called Frog-hoppers 



1 "Insect Architecture," 155. 



