ANNTJLOSA : GEPHYREA. 159 



ANNULOSA. 



CHAPTER XXVIII. 



ANNUL OS A. 



1. GENERAL CHARACTERS OF ANNULOSA. 2. GENERAL CHARAC- 

 TERS OF ANARTHROPODA. 3. CLASS GEPHYREA. 4. GENERAL 

 CHARACTERS OF THE CLASS ANNELIDA. 



SUB-KINGDOM ANNULOSA. The members of this sub-kingdom 

 are distinguished by the possession of a body ivhich is composed 

 of numerous segments, or ' somites,'' arranged along a longitudinal 

 axis. A nervous system is always present, and consists of a 

 double cliain of ganglia, running along the ventral surface of the 

 body, and traversed anteriorly by the oesophagus. The limbs 

 (when present) are turned towards the neural aspect of the body. 



.The sub-kingdom Annulosa may be divided into two primary 

 divisions, according as the body is provided with articulated 

 appendages, or not ; these divisions being termed respectively 

 the Arthropoda and the Anarthropoda. The first of these 

 comprises Crustaceans, Spiders, Scorpions, Centipedes, and 

 Insects ; whilst the latter includes the Spoon- worms, Leeches, 

 Earth-worms, Tube- worms, and Sand-worms. 



DIVISION I. ANARTHOPODA. In this division of the Annulosa, t 

 the locomotive appendages are never distinctly jointed or articu- 

 lated to the body. In this division are included three classes, 

 viz. : the Gephyrea, the Annelida, and the Ghcetognatha. 



CLASS I. GEPHYREA ( = Sipunculoidea). This class includes 

 certain worm-]ike animals in which the body is sometimes 

 obviously annulated, sometimes not ; but there are no ambu- 

 lacral tubes nor foot-tubercles. The nervous system consists of 

 a gangliated cord placed along the ventral surface of the body. 



The Sipunculus, and its allies, make up this class, and from 

 their affinity to the worm-like Holuthurians they have often 

 been placed amongst the Echinodermata. They are not, how- 

 ever, provided with an ambulacral system, the integument is 

 not capable of secreting calcareous matter, and there are no 

 traces of any radiate arrangement of the nervous system. 



The Sipunculus is a worm which is found burrowing in the 

 sand of the coasts of most of our European seas, or which 



