TRACHEATA 371 
jointed, and terminates in two claws; between these is the 
pulvillus, a fleshy vesicle with tubular hairs, which secrete a 
sticky fluid. 
The abdomen may be short and conical, or long and 
cylindrical. There is no true ovipositor, but the terminal 
segments are retracted into the preceding, and can be pro- 
truded telescopically. 
The nervous system is very concentrated ; in some families, 
as the Muscipas&, the Hrppoposcrpak, and the OESTRIDAE, there 
is, besides the brain, only one large ganglion; this is situated 
in the thorax, and gives off nerves to the abdomen. 
The alimentary canal has a stalked sucking stomach, which 
opens into the oesophagus. 
The sexes do not show much external differentiation; as a 
rule the eyes in the male are larger, they are sometimes fused 
together. The eggs are smooth, oval, and slightly curved ; 
they are often provided with a micropyle. In the TIPULIDAE, 
the daddy-long-legs (Fig. 209), they are mature when the 
pupal skin is cast, and are laid immediately by the imago. 
The larvae are white, fleshy, cylindrical maggots. They 
may have a distinct head, as in the TIPULIDAE, or a head may 
be absent, as in the Muscipar. In the first case they have 
biting mouth parts and are often parasitic, in the second they 
suck up liquid nutriment. The ova are usually deposited upon 
the food, either animal or vegetable, in which the larvae 
burrow and on which they feed. Many of the larvae are 
aquatic. They change into pupae within the last larval skin, 
—pupa coarctata,—or cast this skin and become moving pupae 
which swim in water—pupa obtecta. 
Sub-order 1. Aphaniptera. 
The PuLiciIpAE.—This is an aberrant order of Diptera; 
it comprises the fleas. These insects have no wings, though 
there are small flat appendages on the meso- and meta-thorax. 
Their legs are large, and are adapted for leaping. The body is 
compressed. There is no labrum; the labium is small, with 
long palps; the mandibles form serrated stylets, and the 
maxillae have palps. The female lays eight to ten eggs, which 
