112 IXVERTEBEATE ANIMALS. 



SUB-KINGDOM IV. ANNULOSA. 



CHAPTER XL 



General Chakacters of the Annulosa — Divisions of the 

 Annulosa — Characters axd Orders of the Scolecida. 



The Annulose animals are characterised by the possession of a 

 usually more or less elongated bocli/, which is bilaterallij symmetrical, 

 instead of being radially disposed. Commonly the body is divided into 

 similar segments, which may he definite or indefinite, and are arranged 

 along an antero-posterior a.ris. Lateral appendages may be present or 

 absent, and when present are bilaterally disposed. A nervous system 

 is present, and consists of one or two ganglia placed in the anterior 

 part of the body, or of a ventrally placed double gangliated chain. 



The sub-kingdom Annidosa may be divided into the following 

 three primary sections, each of which admits of suiSciently definite 

 characterisation : — 



I. Scolecida. — This division includes the parasitic Worms {En- 

 tozoa), the Wheel-animalcules, and some allied forms, and is char- 

 acteiised by the fact that the body is flattened, and either unseg- 

 mented or imperfectly segmented, though the integument may be 

 annulated. A water -vascular system is present, but the water- 

 vessels are not concerned with locomotion. There is no true blood- 

 .system ; and the nervous system consists of one or two cephalic 

 ganglia, and never has the form of a gangliated ventral chain. Lat- 

 eral appendages are almost universally wanting. 



II. Anarthropoda. — This division includes the Spoon -worms 

 {Gephyrea) and the Ringed Worms {Annelida), and is characterised 

 by the fact that the body is composed of a numbei' (often indefinite) 

 of similar or nearly similar segments arranged longitudinally. A 

 "pseudohsemal" sy.steni of vessels is generally present. The nervous 

 system is placed ventrally, and consists typically of a double chain 

 of ganglia, united by longitudinal commissures, and forming an 

 oesophageal collar. Cilia are generally developed. Lateral locomo- 



