38 ELEMENTS OF BIOLOGY. 



generally communicating with the exterior, and often employed in loco- 

 motion. Nervous system radiate. Adult generally more or less star- 

 like or ** radiate" in shape, young usually showing more or less distinct 

 " bilateral symmetry " — that is, showing similar parts on the two sides 

 of the body. Ex. Sea-urchins, Star-fishes, Brittle-stars, Sea-lilies, 

 Sea-cucumbers. 



Class B. Scolecida. — Integument soft, and destitute of calcareous 

 matter. Water-vascular system not assisting in locomotion. Nervous 

 system consisting of one or two ganglia, not disposed in a radiating 

 manner. Body of the adult sometimes flattened, sometimes rounded 

 and wormlike. Ex. Tapeworms, Flukes, Haii-Avorms, Roundworlns, 

 Wheel-.inimalcules. 



Sub-Kingdom IV. — Annulosa. 



Animal composed of numerous definite segments or " somites," ar- 

 ranged longitudinally one behind the other. Nervous system consisting 

 in its typical form of a double chain of ganglia, which are placed along 

 the ventral surface of the body, are united by longitudinal cords, and 

 form a collar round the gullet, a pair of ganglia being primitively de- 

 veloped in each segment. Limbs (when present) disposed in pairs, and 

 turned towards that side of the body on which the main masses of the 

 nervous system are situated (fig. lo). 



/ 



Fig. lo. — Annulosa. A, Diagram of Annulose animal : a Digestive tube, h Heart, 

 c Nerve-chain. B Diagram of the nervous system of one of the Annulosa. 



Division I. Anarthropoda. — Locomotive appctidages {when present) 

 not distinctly jointed or articulated to the body. 



Class A. Gephyrea. — Body cylindrical, not definitely segmented. 

 IMouth usually with a circlet of tentacles. Ventral cord of the nervous 

 system not furnished with ganglia. Ex. Spoonworms. 



Class B. Annelida. — Body cylindrical, definitely segmented. ,A 

 special system of vessels connected with respiration ("pseudohsemal" 



