INTRODUCTION. 



which are placed along the lower surface of the body, and form a collar 

 around the gullet. Limbs (when present) turned toward that side of the 

 body on which the main masses of the nervous system are situated. 



DIVISION A. ANARTHROPODA. Locomotive appendages, when pres- 

 ent, not distinctly jointed or articulated to the body. 

 CLASS I. GEPHYREA. Ex. Spoon-worms (Sipunculus). 

 CLASS II. ANNELIDA (Ringed-worms). 



Order 1. Hirudinea. Ex. Leeches (Sanguisuga, Hirudo). 

 Order 2. Oligochceta. Ex. Earth-worms (Lumbricus), Water- 

 worms (Nais). 



Order 3. Tubicola. Ex. Tube- worms (Serpula). 

 Order 4. Errantia. Ex. Sand-worms and Sea-centipedes (Nereis) , 



Lob-worm (Arenicola), Sea-mouse (Aphrodite). 

 CLASS III. CH^TOGNATHA (Arrow-worms). Ex. Sagitta. 

 /- DIVISION B. ARTHROPODA. Locomotive appendages jointed or articu- 

 lated to the body. 



CLASS I. CRUSTACEA. Respiration aquatic, mostly by gills. Two 

 pairs of antennae. Limbs more than four pairs in number, carried upon 

 the thorax, and generally upon the abdomen also. 

 Order 1. Ichthyophthira. Ex. Lernaea. 

 Order 2. Rhizocephala. Ex. Peltogaster. 

 Order 3. Cirripedia. Ex. Barnacles (Lepas), Acorn-shells (Bal- 



anus). 



Order 4. Ostracoda. Ex. "Water-fleas (Cypris). 

 Order 5. Copepoda. Ex. Cyclops. 



Order 6. Cladocera. Ex. Branched-horned Water-fleas (Daphnia). 

 Order 7. Phyllopoda. Ex. Brine-shrimp (Artemia). 

 Order 8. Trilobita (Extinct). 



Order 9. Merostomata. Ex. King-crabs (Limulus). 

 Order 10. Lcemodipoda. Ex. Whale-louse (Cyamus). 

 Order 11. Isopoda. Ex. Wood-lice (Oniscus), Slaters (Ligia). 

 Order 12. Amphipoda. Ex. Sandhopper (Talitrus), Fresh-water 



Shrimp (Gammarus). 



Order 13. Stomapoda. Ex. Locust-shrimp (Squilla). 

 Order 14. Decapoda. Ex. Lobster (Homanis), Cray-fish (Astacus), 

 Shrimps (Crangon) ; Hermit-crabs (Pagurus) ; Crabs 

 (Cancer, Carcinus), Land-crabs (Gecarcinus). 



CLASS II. ARACHNID A. Respiration aerial, by pulmonary chambers 

 or air-tubes (tracheae) in the higher forms. Antennae converted into 

 jaws. Head and thorax amalgamated. Four pairs of legs. Abdomen 

 without limbs. 



Order 1. Podpsomata (Sea-spiders). Ex. Pycnogonum. 



Order 2. Monomerosomata. Ex. Mites (Acarus), Water - mites 



(Hydrachna), Ticks (Ixodes). 

 OrderS. Adelarthrosomata. Ex. Harvest - spiders (Phalangidae), 



Book-scorpions (Chelifer). 

 Order 4. Pedipalpi.Ex. Scorpions (Scorpio). 



