77?^ Method of Ovipositing. 119 



plicated, can be divided into three stages, (i) The canal 

 is bored, the ovipositor gliding under the imbricated 

 scales to the base of the bud, and then being driven into 

 the centre of the bud-axis. (2) The Qgg passes out of 

 the ovarium to the base of the ovipositor, where the egg- 

 stalk is pinched between the two spiculae, and the tg^ 

 is pushed along the ovipositor. (3) After the point of 

 the ovipositor is withdrawn, the egg-body enters the 

 pierced canal, and is pushed forward by the ovipositor 

 until it reaches the bottom. 



If we consider all this varied procedure, we cannot 

 but be astonished at the accuracy with which the fly 

 carries it out, and repeats it many times in succession. 

 Only one egg can ever pass through the same canal ; 

 there is no room for a second, because the egg-stalk of 

 the first egg remains lying in the canal. 



Those flies which lay their eggs in leaf surfaces have 

 naturally a much easier task, since they have only to 

 pierce a thin membrane. The mechanism of ovipositing 

 however is exactly the same. 



We shall next consider a provision existing in the 

 terebra, by which the fly is enabled to carry out all the 

 operations required in ovipositing, with the greatest 

 exactitude. For this purpose its rigid chitinous armour 

 is furnished with tactile hairs at various points. The 

 tactile organs peculiar to insects consist of fine hairs, 

 connected at their bases with ganglionic swellings of 

 sensory nerve-matter, and they are found at various 

 parts of the ovipositing apparatus. They occur con- 

 stantly, in all hymenoptera, on the arch of the anterior 

 plate. Their number varies in different species from 



