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 fine 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. 
CHARACTERISTICS. — Hymenoptera with a well-developed ovipositor 
which sometimes functions as a borer. The abdomen 1s 
sessile. The larvae feed on plants, and resemble cater- 
pulars. 
Family UrocertpaE (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-flies)—This is a numerous 
