24 AN ACCOUNT OF BRITISH FLIES. 
Genus 1.—PULEX. 
Characters of the Genus.—Body oval and compressed, and covered 
by a hard, chitinous integument, which is covered by hairs and 
bristles on the back and legs. There are thirteen segments, and 
they are continuous, there being no distinction into thorax and 
abdomen. 
Head small. Mouth suctorial. Upper lip obsolete (unless the 
lingua represents it) The mandibles are in the form of two flat 
sete, with a central rib and serrated edges. The lingua is the same 
length as the mandibles, the three forming a piercing, or puncturing 
Fic. 3.—Imago of Pulex $.—a, antennz ; m/¢, maxillary palpi ; 2, zz, zzz, pro-, 
meso-, and meta-thorax. 
organ. When at rest these organs are closed by the labial palpi, 
which form a tubular Aaustellum. These arise from a small labium, 
which comes from a very small mentum. 
The maxillz are sub-triangular appendages, and are coriaceous 
and are situated at the side of the mouth. They have large maxillary 
palpi arising from the base, composed of four joints, and formerly 
mistaken for antenne. 
Eyes small (=simple ocelli) and round. Antennz are placed in 
pits behind the eyes. These pits are covered by movable valves, 
At times the antennz may be withdrawn out of these cavities. 
They are four-jointed appendages, the third joint being small and 
cup-shaped. The terminal joint is often transversely striated.* They 
vary in different species. 
The thorax is composed of three typical segments, but more 
distinctly marked than in other insects. On the second, or meso- 
thoracic, is the first pair of scales, or rudimentary wings, and on the 
metathoracic segment we find the large scales representing the hind 
* These striations are really joints. 
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