THE HYMENOPTERA 339 



connected with egg-laying, it may have projections along its lower edge 

 and be used like a saw to cut slits in leaves or other structures in which 

 to insert the eggs. In other cases it becomes a sort of boring organ used 

 in making holes in leaves, stems, wood, or animals, in which the eggs are 

 placed. Sometimes the ovipositor is very prominent and is not retractile, 

 while in other species it can be drawn entirely within the body. In a 

 large section of the order, however, regarded as containing the more 

 highly developed members of the group, deposition of the eggs is not 

 within objects but on surfaces, and a hole being no longer needed, the 

 ovipositor has become modified in most cases, glands connected with it 

 produce a. more or less poisonous fluid (possibly it is more or less poison- 

 ous in the lower forms also) and the sting is thus produced, a structure no 

 longer needed for its original purpose having been transformed into a 

 weapon for defense. In the ants, however, various degrees of reduction of 

 this structure occur, some ants having no stinging power whatever while a 

 few are quite effective in this way. From these facts the reason why drone 

 bees and the males of the other Hymenoptera are harmless, is evident. 



The two sections of the order thus distinguished, are called the 

 Terebrantia or boring, and the Aculeata or stinging Hymenoptera. 

 Another distinction also separating these divisions may be seen by an 

 examination of the mouth parts. In the Terebrantia these are quite 

 typical chewing organs, but in the. Aculeata the maxillse and labium 

 have been modified to form organs for sucking and lapping up fluids, 

 though the amount of this modification differs in different families. 

 A third distinguishing feature is that in the Terebrantia the hind leg 

 has two trochanters while in nearly all the Aculeata there is only one. 



Development in this order is by a complete metamorphosis. The 

 larvae differ much in appearance in the various families, some feeding 

 on leaves and greatly resembling caterpillars. Others are borers in 

 wood and are modified to adapt them to life under such conditions. 

 Still others, particularly those which are parasitic within the bodies of 

 other insects, may be so changed as to make it seem almost impossible 

 that they can be insect larvae. Many of those living on food provided 

 for them during this stage of their existence greatly resemble and are 

 sometimes called maggots. At pupation a marked change in appearance 

 takes place, antennae, legs, wing stubs and body characters nearly like 

 those of the adults now showing, and the legs and antennae project, en- 

 cased by sheaths of the pupa skin, the pupa in this order being a pupa 

 libera as already described for some beetles (see page 99, and Fig. 30). 



The characters by which Hymenoptera may be recognized are: 



Insects which when adult have in most cases, four membranous wings 

 with few or even no cross veins, the hinder pair the smaller. Mouth parts 

 for chewing, or for chewing and also for sucking. The females have in nearly 

 all cases either an ovipositor or a sting. The metamorphosis is complete. 



