18 ZOOLOGY. 



of ganglia (Gr. ganglion, a knot) placed in each ring or 

 segment, and connected by two nervous cords or commis- 

 sures (Lat. committo, to join together), which run along 

 the whole ventral surface of the body. The first or front 

 pair of ganglia, is always situated above the alimentary 



FIG. 2. DIAGRAM OF AN ANNULOSE ANIMAL. 

 a, haemal or blood system; b, neural system; c, digestive system. 



tube, and the nervous cords connecting this with the 

 second pair pass round the gullet, and are in consequenco 

 termed the (BSOphageal collar. The nervous system is 

 lodged in the same cavity as the digestive and circulatory 

 organs, the body walls forming a single tube (see fig. 1). 



The alimentary canal has always two openings, and is 

 completely shut off from the cavity of the body. 



DIVISIONS OP THE ANNULOSA. 



15. The sub-kingdom Annulosa comprises two great 

 divisions the Arthropoda (Gr. arthros, a joint; podes, 

 feet), or animals with jointed limbs, and those in which 

 these appendages are absent. The latter have been termed 

 Anarthropoda (Gr. an, without). 



The Arthropoda comprise : 



1. Insecta (Bees, Butterflies, &c.) 



2. Myriapoda (Centipedes, &c.) 



3. Arachnida (Spiders, &c.); and 



4. Crustacea (Crabs, Lobsters, &c.) 



The principal characteristic of this group is the posses- 

 session of three or more pairs of jointed limbs composed 

 of the chitinous substance described above, These limbs 



