250 ARTHROPODS. 



abdominal appendages of the male are strongly developed, those 

 of the female are weak except the last, which in both sexes form 

 paddles. They are marine forms, e.g., — Mysis (without gills on the 

 thoracic legs), Lophogaster and Euphaitsia (with gills on the 

 thoracic legs). The last named starts in life as a Nauplius. As 

 an adult it has numerous phosphorescent organs. 

 Order 4. Decapoda. The shield is largd and firm, and is fixed to the 

 dorsal surface of all the thoracic segments. Of the thoracic 

 appendages, the first three pairs are maxillipedes, the five other 

 pairs are walking-legs (whence the term Decapod). 

 Sub-order i. Macrura. Abdomen long. Homarus (lobster) ; 

 Nephrops (Norway-lobster, sea-crayfish) ; Astactis, (fresh- 

 water crayfish ; Falinurus (rock-lobster), whose larva was 

 long known as the glass-crab (Phyllosomu) ; Penceus a shrimp 

 which passes through Nauplius, ZoEea, and Mysis stages ; 

 Lucifer and Ser/^estes are also hatched at a stage antecedent to 

 the ZoEea ; Crangon vulgaris (the British shrimp) ; Palcemon, 

 Pandalus, Hippolyte (prawns) ; Galathea (with the abdomen 

 bent inwards) ; Pagurus, Eupagurus (hermit-crabs) ; Birgus ■ 

 latro (the terrestrial robber or palm-crab). Opinion seems to 

 incline against recognising a separate sub-order (Anomura) for 

 the soft-tailed hermit-crabs. 

 Sub-order 2. Brachyura. Abdomen short, and bent under the 

 cephalothorax. Ca»f^r (edible crab); Carcinus mmnas (gteen 

 shore-crab) ; Portunus (swimming-crab) ; Maia (spider-crab) ; 

 Lithodes (stone-crab) ; Porcellana ; Droniia (often covered by 

 a sponge) ; Pinnotheres (living inside bivalves) ; Gelasimus 

 (fiddler-crab, a very adept burrower) ; Telphusa (a fresh-water 

 crab) ; Gecarcinus (land-crabs, only visiting the sea at the 

 breeding season). 



Second Set of Arthropoda — Tracheata, including four 

 Classes : — 



1. PROTRACHEATA. i. MVRIOPODA. 3. INSECTA. 4. AraCHNOIDEA. 



Peripatus alone. Centipedes and or He-tapoda. Scorpions, Spiders 



Millipedes. Mites, King-crab, etc. 



y ' ^- — .^ ' 



with pre-oral antennse (Antennata). A heterogeneous class, 



but with no preoral 

 antennae (Chehcerota). 



• General Characters of Tracheata. 



Most of the Tracheata live on land or in the air, but there 

 are exceptions, e.g., those larval insects which live in fresh 

 water, and the king-crab which is marine. 



The typical respiratory structures are air-tubes or tracheae, 



