HYMENOPTERA. 
*5 
greater number of their legs; these varying from twenty to twenty-two, whereas 
those of the Lepidoptera have but sixteen at most. They also differ by the shining 
and almost naked skin, and the curious habit possessed by many of curling in the 
posterior segments, raising them at the same time and depressing them with a 
rhythmic movement. This action, which may be for the purpose of frightening 
away foes, coupled with the melancholy-looking eyes, gives them a grotesque 
appearance, not observable in the caterpillars of the Lepidoptera, save in a few 
instances. When full grown, the majority of the larvae leave the food-plant and 
spin in or on the surface of the ground, or under dry leaves and moss, a barrel¬ 
shaped cocoon in which they pass the winter, turning to a chrysalis only a short 
1, Sirex juvencus, female larva, pupa (all of nat. size); 2, CORN saw-fly and larvae in the rye stalks ; 
3, Pacliymerus calcitrator, a wasp parasitic on the above ; 4, Larva and pupa of Cephus (enlarged). 
time before the perfect insect emerges. At least a thousand species are known, 
though this is probably but a small moiety of those that exist. 
Stem Saw-Flies,—F amily Cepiiid^e. 
The larvae of these slender, delicate, armoured insects pass their lives in the 
stems of plants or young shoots of trees ; and the adults are characterised by the saw 
of the female being partially concealed by two integumental flaps. As an example 
of the typical genus, we may take the corn saw-fly (Cephus pygviceus), of which 
the perfect insect flies actively in the sunshine, flitting from blossom to blossom 
among buttercups in May, and thence onwards through the summer. The larvae 
cause serious damage on the Continent to rye crops, and more rarely in wheat fields, 
where they crawl up and down within the stems, feeding on the delicate tissues. 
When full fed, they construct a transparent cocoon in which to pass the winter, 
