THE GALL-FLIES. i245 



and the abdomen is short and very much compressed. 

 It is in the structure of this part of the body, and of 

 the ovipositor, that tliese insects principally differ 

 from the ordinary parasitic Spiculifera. The greater 

 portion of the surface of the abdomen is occupied 

 by the second segment, considering the very small 

 peduncle as the first ; the remainder of the segments 

 are much smaller, forming narrow rings one behind 

 the other. The apical segment is thrown down 

 almost entirely to the ventral surface, where it forms 

 a cleft plate enclosing the ovipositor, which exhibits 

 a most remarkable construction. Instead of being 

 confined to the apex of the abdomen, it extends for- 

 wards nearly to the base of that region of the body, 

 where there is a cavity for its reception, enclosed not 

 only between the lateral plates of the abdomen, but 

 also by a pair of broad valves, thetfasal joints of the 

 ordinary sheath of the ovipositor. The second joints 

 of this sheath project along with the ovipositor through 

 the cleft apical segment of the abdomen, as in the 

 Ichneumons and Saw-flies. The o^dpositor itself, 

 which is an exceedingly fine bristle-like organ, con- 

 sists of precisely the same parts as that of the 

 Ichneumons, namely a superior channeled bristle, 

 and a pair of still more delicate filaments lying in 

 the furrow presented by this for their reception. 



With this curious instrument, which is of great 

 length compared with the size of the insect, the female 

 punctures the tissues of living plants, introducing 

 one or more eggs into each place which she attacks. 

 But the most singular circumstance is, that the irri- 

 tation produced by this minute puncture causes an 

 immediate morbid growth in the part affected, the 

 result of which is an excrescence of larger or smaller 



