SUB-KINGDOM V. MOLLUSCA. 39 



vessels). A gangliated ventral nerve-chain. Ex. Leeches, Earth- 

 worms, Tubeworms, Sandworms, 



CLASS C. CH^TOGNATHA. Head furnished with rows of bristles. 

 Nervous system consisting of a cephalic and a ventral ganglion united 

 by cords which form a collar round the gullet. Ex. Sagitta. 



DIVISION II. ARTHROPODA. Locomotive appendages jointed or arti- 

 culated to the body. 



CLASS D. CRUSTACEA. Respiration aquatic, by the general surface 

 of the body or by gills. Two pairs of antennas. Locomotive appen- 

 dages more than four pairs in number, carried upon the thorax, and 

 mostly the abdomen also. Ex. Crabs, Lobsters, King-crabs, Wood- 

 lice. 



CLASS E. ARACHNIDA. Respiration aerial, by the surface of the 

 body, by pulmonary chambers, or by air-tubes ("tracheae"). Antennas 

 converted into jaws. Head and thorax amalgamated. Four pairs of 

 legs. Abdomen destitute of limbs. Ex. Spiders, Scorpions, Mites, 

 Ticks. 



CLASS F. MYRIAPODA. Respiration aerial, by air-tubes (tracheae) 

 or by the skin. Head distinct ; remainder of the body composed of 

 nearly similar segments. Legs more than eight pairs in number, and 

 borne partly by the abdomen. One pair of antennae. Ex. Centipedes 

 and Millipedes. 



CLASS G. INSECTA. Respiration aerial, by air-tubes (tracheae). 

 Head, thorax, and abdomen distinct. One pair of antennae. Three 

 pairs of legs borne on the thorax. No locomotive limbs on the segments 

 of the abdomen. Ex. Beetles, Flies, Butterflies. 



SUB-KINGDOM V. MOLLUSCA. 



Animal soft-bodied, usually with a hard covering or shell. Not 

 exhibiting distinct segmentation. Nervous system consisting of a single 

 ganglion or of scattered pairs of ganglia. A distinct heart and breath- 

 ing organ, or neither (fig. n). 



DIVISION I. MOLLUSCOIDA. Nervous system consisting of a single 

 ganglion or a principal pair of ganglia. No heart, or an imperfect 

 one. 



CLASS A. POLYZOA. Animal always forming compound growths or 

 colonies. No heart. The mouth of each member of the colony sur- 

 rounded by a circle or crescent of ciliated tentacles. Ex. Sea-mat. 



CLASS B. TUNICATA. Animal simple or compound, enclosed in a 

 leathery or gristly case. An imperfect heart. Ex. Sea-squirt. 



CLASS C. BRACHIOPODA. Animal simple, enclosed in a bivalve 

 shell. Mouth furnished with two long fringed processes or "arms." 

 Ex. Lamp-shells. 



