The Method of Ovipositing. 115 



quite evident that the anterior plate remains always a 

 fixed point, while on the contrary the posterior plate 

 is drawn alternately up and down. By these simple 

 movements of the posterior plate, the insertion and 

 withdrawal of the spiculae are carried on ; the thrusting 

 out of the spiculae is the harder operation, and is 

 effected by two powerful muscles ; while their with- 

 drawal is easier, and requires only one muscle. The 

 anterior plate remains passive during the act of ovi- 

 positing, therefore the seta, which is firmly united 

 to it, takes a less active part ; it is pushed steadily 

 forward by the fly and is driven into the canal that has 

 been bored and opened by the spiculae. 



We must next inquire into the manner in which the 

 gall-fly introduces the ^^% into the bud by means of 

 this apparatus. Hartig's explanation, which has hitherto 

 been received, was that the extremely ductile &%^ was 

 driven through the ovipositor itself. He thought 

 that the contents of the egg passed into the egg-stalk 

 and were collected in its club end, but after the real 

 egg-body had been thrust into the plant tissue, the 

 contents streamed back again into it. Hartig thought 

 this theory all the more probable, because the passage 

 of the yolk into the egg-stalk could actually be observed 

 in the eggs of the Cynipidae. This is easily seen under 

 the microscope if the ^%%, taken from the ovary, be 

 examined in water. We shall refer later to the mean- 

 ing of this phenomenon, when we come to compare the 

 length of the egg-stalk with that of the ovipositor, but 

 Hartig's theory must be abandoned as unsatisfactory. 



In every case the ovipositor is considerably longer 



I 2 



