4. Pediculus.   Louse,

Antenna length of the thorax. Legs six, formed for walking. Mouth producing a sting. Abdomen depressed, and appears as if formed of different lobes.

5. Pulex.   Flea.

Antennae filiform. Legs six, formed for leaping. Eyes two. Trunk taper, bent, concealing the sting Abdomen compressed.

6. Acarus.   Mite.

Legs eight. Eyes two, situated on each side of the head. Feelers two, jointed, leg-shaped.

7. liycfraclina.   Hydraclma.

[lead, thorax, and abdomen united. Feelers two, jointed. Eyes two, four, or six. Legs eight, formed for Swimming.

8. Plialangium.   Phalangium.

Antenna fixed to the fore-part of the head, and nade like the feet. Legs eight. Eyes, two on the summit of the head, and two on the sides. Abdomen round.

9. Aranea.   Spider.

Legs eight. Eyes eight. Feelers two, jointed; the
tips of which, in the male, distinguish the sex. Mouth
furnished with two hooks. `Abdomen terminated by
papilla,