1 1 -2 INVEIITEBliATE AXJMALS. 



SUB-KINGDOM IV. ANNULOSA. 



CHAPTER XI. 



GeNER.1L C'H.iRACTERS OF TIIK AxNULOSA — DIVISIONS OF THE 

 AnNULOSA — (^'lIARACTERS .VND ORDERS OF THE 8cOLECIDA. 



The Anmilose animals are cliaiacterised by the possession of a 

 vsiMiJI>i muri: or less elongated hodi), v:Itieh is bilaterall)/ si/mmetrical, 

 insteiid of hei/if/ niiliidli/ disposal. Coriiriionhi the hody is divided into 

 siinilor seijnients. irliieli nxiii he dcfinitK or indejinite, and are arranged 

 along an ontero-jjosteri<ir a.eis. Lateral appendetges nunj he piresent or 

 absent, and u'hen. piresent are hilateralli/ disposed. A nerrons si/.stem 

 is present, and ennslsts nf ane or tn-n i/anglirx plaeed in tlie anterior 

 part of tli.e /«"'//, or of a rent rail y [ilae<:d donjile gangliated ehain. 



The sub-kiiigdoiii Anjmlosa may V>e divided into the following 

 three primary sections, each of which admits of sufhciently detinite 

 characterisation : — 



I. ScoLECiDA. — Tliis di\dsion inchides the j)arasitic Worms {En- 

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

 acterised by tlie fact that the liody is flattened, and either unseg- 

 mented or imperfectly segmented, though the integument may be 

 annulfited. A water -vascular sj'stem is jiresent, liut 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 lias the foiin of a gangliated ventral chain. Lat- 

 eral .ajjpendages arc almost luuversally wanting. 



II. Anarthropoiia. — This ilivision includes the Sjioon-worms 

 {Gepjhiirea) and the Itiiiged Wuiins (A nnelid.a), and is characterised 

 by the fact that the liody is com|iosed of a number (often indefinite) 

 of similar or nearly .similar segments arranged longitudinally. A 

 " ]iseudi)liicni.-d" system nf vessids is generally Jiresent. The nervous 

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

 <'f Lf.innlia, united by longitudinal commissures, and forming an 

 (j.so|ili:ig('.il collar. Cilia are generally developed. Lateral locomo- 



