150 Knapweed Gall -flu 



The first segment of the ovipositor (which appears as the terminal 

 segment of the abdomen) is about 2 '7 mm. long ; it is swollen anteriorly, 

 being about 0'6 mm. across in this region, and it becomes narrower in 

 the posterior portion ; near the distal end it is about 0-25 mm. in 

 diameter. The w^alls are strongly chitinised and it is covered with 

 numerous hairs. 



The second or middle segment of the ovipositor is about 2-3 mm. 

 in length, by 0-15 mm. wdde along its whole length, and consists of 

 a transparent flexible membrane in which a great number of small 

 chitinous sclerites are partially embedded. This segment is capable 

 of protrusion and retraction, like the finger of a glove. 



-•.■<; 



Fig. 1. Extended ovipositor of U. solstitialis from left side, x 15. 1, 1st segment of the 

 ovipositor ; 2, 2nd, flexible segment ; 3, 3rd, piercing segment 



The third and last segment is the actual piercing portion of the 

 ovipositor ; it is composed of chitin, is about 2-3 mm. long, and except 

 at the extreme narrow tip is about 0-07 mm. in diameter. There are 

 two sharp-cutting blades at the sides of the tip. This segment contains 

 the terminal portion of the oviduct, which opens to the exterior near 

 the tip. During the passage of the ova this segment probably expands 

 slightly. 



The ovipositor is extended by pressure, presumably by muscular 

 compression acting on some of the body-fluids. If the swollen portion 

 of the ovipositor is compressed with a pair of forceps, the flexible and 

 piercing segments are readily everted, and they always assume a curved 



