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tube. The latter consists of a slender but very stout rod, 

 serrated distally (fig. 22), whose function is to bore through 

 the fly-pupa prior to oviposition, the. -eggs entering the hole 

 through a tube formed between this rod and tho pair of first 

 appendages which partly surround it. The proximal portion 

 of these first appendages has grown in a strong curve, as 

 described above, into the abdomen of the wasp ; a second piece 

 growing forwards and downwards from the end of this has 

 also been described above. These structures likewise chitinise 

 and produce an exceedingly efiicient system of phragmas. 

 The insect has, as it were, taken full advantage of this, and 

 a great group of muscles has developed, whose function is to 

 move and hold the ovipositor while the latter is functioning. 

 These muscles are shown in fig. 22. One group radiates out 

 from the base of the second appendages, and is inserted on 

 to the first portion of the phragma. Other muscles are 

 inserted into the descending portion of the phragma; others, 

 again, are attached to the base of the ovipositor. A system of 

 smaller phragmas is also developed on the ventral body wall 

 to give firmer attachment to the "origin" of these muscles. 

 The figure, however, will make this elaborate system of muscles 

 clearer than any verbal decription can. 



The action of the ovipositor is now obvious ; a pull by the 

 muscles of the great phragmas will immediately swing the 

 o^^Lpositor forward out of its sheath (third appendage) into a 

 vertical position, and the prolonged contraction of these and 

 other muscles holds the ovipositor very rigidly for several 

 minutes, during which the upward and downward movement 

 of the abdomen causes the rigidly fixed ovipositor to bore its 

 way through the hard sheath of the unfortunate fly-pupa. 



It is worth noting here, that during the development of 

 the abdominal imaginal discs, the eleventh body segment (sixth 

 abdominal) grows backwards a considerable distance along 

 the ventral body wall and overlaps more than half the anterior 

 portion of the ovipositor. During oviposition, consequently, 

 when the very flexible abdominal segments are subjected to 

 considerable strain, the ovipositor pushes these overlaps for- 

 wards and has, then, th^ appearance of arising from a 

 pyramidal structure on the ventral side of the body. No such 

 structure is, of course, normally present. 



The histological changes which underlie this development 

 will be referred to under ''the integument." 



The devolpment of the ovipositor of Locusta has been 

 described by Dewitz (1875). He describes an anal segment 

 bearing a pair of appendages (cerci) homologous probably with 

 the sensory papillae of Nasonia. The ovipositor is developed, 

 according to Dewitz, from the three preceding segments, one 

 K 



