TRACHEATA 377 



complex brain, two thoracic ganglia, and five or six abdominal. 

 The alimentary canal is long, with large salivary glands, and a 

 suctorial stomach, or, in the ants, a gizzard. The number of 

 Malpighian tubules is great, 20 to 150. 



With few exceptions, the larvae are apodal white grubs, 

 living either parasitically in the bodies of other insects, or in 

 plant galls, or in special cells prepared for their reception. In 

 two families, however, they resemble in appearance and habits 

 the caterpillars of the Lepidoptera. As a rule, the larvae 

 have a retractile head, with short mandibles, maxillae, and 

 labium. The pupae are mostly surrounded by a silken cocoon. 



The wax-secreting apparatus consists of numerous glands, 

 mostly unicellular, which open to the exterior by iine chitinous 

 tubes. The wax of bees is secreted in fine transparent plates 

 on the under surface of the abdomen. 



The order may be divided into three sub-orders : 



1. Phytophaga. 



2. Entomophaga (Parasitica). 

 .3. Aculeata. 



Sub-order 1. Phytophaga. 



Chai!ACTEEISTICS. — HymcTUiptera with a well-developed ovipositor 

 which sometimes functions as a horer. The abdomen is 

 sessile. The larvae feed on plants, and resemble eater- 

 pillars. 



Family Ueoceeidae (Wood-wasps). — The insects are large 

 for Hymenoptera, with elongated bodies. The abdomen of the 

 female terminates in a long ovipositor, with which she bores 

 holes into wood to deposit her eggs there. The larvae are 

 white grubs, with three pairs of very small legs and strong 

 mandibles ; they eat out passages in the wood, and form 

 silken cocoons mixed with sawdust, in which the pupal stage 

 is passed. The complete insect emerges in these galleries, 

 and eats her way through the bark to the outside world. 



Sirex gigas, one of the largest of these insects, attacks in 

 this way the wood of Conifers. Sirex juvencus is a smaller 

 species. 



Family Tenthredinidae (Saw-fiies). — This is a numerous 



