892 AN INTRODUCTION TO ENTOMOLOGY 



A similar form of the abdomen is also characteristic of the second 

 suborder, the Idiogastra, except that the tergmn of the first abdominal 

 segment is not longitudinally divided. But this suborder can be dis- 

 tinguished from the Idiogastra by the characters given in the table 

 above. 



There are no wingless forms of the Chalastogastra. In tne more 

 generalized members of the suborder nearly all of the wing-veins are 

 preserved, although the courses of the branches of the forked veins 

 have been greatly modi^ed, as indicated on an earlier page, and as is 

 shown in the figures of wings given later. 



The ovipositor of the females is well developed and complicated 

 in structure. It is fitted for making incisions in the leaves or stems 

 of plants and is more or less saw-like in form. It is this fact that 

 suggested the common name sawfiies which is applied to members of 

 this order. 



The ovipositor and its sheath consists of three pairs of appendages 

 or gonopophyses ; one pair arising from the stemiim of the eighth 

 abdominal segment and two pairs from the sternum of the ninth 

 abdominal segment. The outer pair of the ninth abdominal segment 

 constitute the sheath of the ovipositor so called because when the 

 ovipositor is not in use it is enclosed between the two members of 

 this pair of gonopophyses. The ovipositor is a double organ, con- 

 sisting of two similar blades situated side by side. Each blade con- 

 sists of two gonopophyses, an upper or posterior one, known as the 

 support or lance, and a lower or anterior one, the so-called saw or 

 lancet. The supports are the inner gonopophyses of the ninth ab- 

 dominal segment, and the saws are the gonopophyses of the eighth 



abdominal segment. 



Although each of the saws 

 is closely joined to its support 

 it can be moved backward and 

 forward along it. Figure 1132 

 represents one of the blades of 

 the ovipositor of Cimbex amer- 



The ovipositor of this saw- 

 Fig. 1 132.— Blade of ovipositor of Cimbex fly is fitted for cutting slitS in 

 americana; a, support ; b, lancet. leaves in which the eggs are de- 



posited . In those members of 

 this suborder that deposit their 

 eggs in the stems of plants or the trunks of trees, as the Siricidge, the 

 ovipositor is slender and long. After a slit has been cut or a hole 

 drilled in the trunk of a tree, as the case may be, an egg is forced down 

 between the blades of the ovipositor to the nidus prepared for it. 



The larvae of the Chalastogastra are all plant -feeders. With the 

 exception of those that are leaf-miners they are caterpillar-like in form. 

 Prolegs are present in the Xyelidas, Cimbicidas, Tenthredinidas and 



