The Method of Ovipositing. 121 



canal of the seta, are distributed to these organs of 

 touch. In consequence of this provision, the fly uses 

 the ovipositor as a feeler, and chooses with precision 

 the spot in which the ^gg is to be deposited. The fly 

 would otherwise fail to find within the bud either the 

 region of the rudimentary leaves, or the meristem in 

 which it is essential that the egg be placed, to secure 

 subsequent gall formation. 



A further proof of the delicacy of feeling possessed 

 by gall-flies is shown by the fact, previously mentioned, 

 that many species prick flower-buds only. Here, it is 

 true, the fly also uses its antennae in selecting the buds. 

 If we observe an Aphilotrix fecimdatrix "which, has been 

 brought indoors upon a detached bough, we shall see 

 that it is by careful feeling that she finds out the flower- 

 buds, to prick them. Certainly it may happen that 

 she lays an egg occasionally in a leaf-bud, but as if she 

 had found out her mistake, she immediately quits the 

 leaf-bud. During these experiments I tried to find out 

 if it was possible to distinguish between a leaf-bud and 

 a flower-bud, and I discovered that there were certain 

 appreciable differences between them. In flower-buds 

 the mass of rudimentary stamens gives the bud a larger 

 circumference than that of one which contains leaf rudi- 

 ments. Now in one bud all the leaf rudiments may be 

 supplanted by pollen rudiments, or they may occur 

 together. The greater the proportion of pollen rudi- 

 ments found in a bud, the more altered is its contour, 

 and the whole bud has quite a different appearance ; 

 it is thicker in the middle, and more slender at the apex 

 than other buds. I tried to guess before-hand whether 



