20 INTRODUCTION. 
Crass I. CRUSTACEA.—Respiration aquatic, mostly by gills. Two 
pairs of antennze. Limbs more than four pairsin number, carried upon 
the thorax, and generally the abdomen also. 
Order 1. Rhizocephala.—x. Peltogaster. 
Order 2. Lchthyophthira.—Ex. Lernea. 
Order 3. Cirrifedia. — x. Barnacles (Lepas), Acorn - shells 
(Balanus). 
Order 4. Ostracoda.—x. Water-fleas (Cypris). 
Order 5. Copepoda.—Lx. Cyclops. 
Order 6. Cladocera.—L£x. Branched-horned Water-fleas (Daph- 
nia). 
Order 7. Phyllofoda.—Ex. Brine- sarap (Artemia). 
Order 8. 7Zrilodbita (extinct). 
Order 9. Merostomata.—£x. King-crabs (Limulus). 
Order 10. Lemodipoda.—Lx. Whale-louse (Cyamus). 
Order 11. Zsopoda.—Ex. Wood-lice (Oniscus), Slaters (Ligia). 
Order 12. Amphijoda. — Ex. Sandhopper (Talitrus), Fresh- 
water Shrimp (Gammarus). 
Order 13. Stomapoda.—x. Locust-shrimp (Squilla). 
Order 14. Decapoda. — Hx. Lobster (Homarus), Cray - fish 
(Astacus), Shrimps (Crangon) ; Hermit-crabs (Pa- 
gurus); Crabs (Cancer, Carcinus), Land-crabs 
(Gecarcinus). . 
Crass II. ARACHNIDA.—Respiration aerial, by pulmonary chambers 
or air-tubes (trachez) in the higher forms. Antennz converted into 
jaws. Head and thorax amalgamated. Four pairs os legs. Abdo- 
men without limbs. 
Order 1. Podosomata (Sea-spiders).—Zx. Pycnogonum. 
Order 2. Monomerosomata.—Ex. Mites (Acarus), Water - mites 
(Hydrachna), Ticks (Ixodes). 
Order 3. Adelarthrosomata,— Ex. Harvest-spiders (Phalangide), 
Book-scorpions (Chelifer). 
Order 4. FPedipal~:.—Ex. Scorpions (Scorpio). 
Order 5. Araneida.—Ex. WHouse -spiders (Tegenaria), Field- 
spiders (Epeira). 
Crass III. Myriapopa. — Respiration aerial, by tracheze (air- 
tubes) or by the skin. Head distinct ; remainder of body composed of 
nearly similar segments; legs more than eight pairs in number, and 
borne partly upon the abdomen. One pair of antenneze. 
Order 1. Chilopoda.—LEx. Centipedes (Scolopendra). 
Order 2. Chilognatha.—Lx. Millipedes (Iulus). 
Order 3. Pauropoda.— Ex. Pauropus. 
Cuass IV, INsEcTa. — Respiration aerial, by trachese. Head, 
thorax, and abdomen distinct. One pair of antennz. ‘Three pairs of 
legs, and generally two pairs of wings on the thorax. No locomotive 
limbs on the abdomen. 
Order 1. Anoplura.—Ex. Lice (Pediculus). 
