136 ANNULOSA. 



CHAPTER XIII. 



SUB-KINGDOM IV. ANNULOSA. 

 FOSSIL ANNELIDA. 



SUB-KINGDOM ANNULOSA. The Annulose animals are distin- 

 guished by the possession of a body which is composed of numer- 

 ous segments arranged longitudinally one behind the other. A 

 nen>ous system is always present, and consists of a double chain 

 of ganglia running along the ventral surface of the body and 

 traversed anteriorly by the gullet. The limbs (when present] are 

 turned toivards that side of the body upon which the chief masses 

 of the nervous system are situated. 



The sub-kingdom Annulosa may be divided into two primary 

 sections, according as the body is provided with articulated 

 appendages or not ; these divisions being known respectively 

 as the Arthropoda (or Articulatd) and Anarthropoda. The 

 first of these comprises the Crabs, Lobsters, and the like (Crus- 

 tacea), the Spiders and Scorpions (Arachnida), the Centipedes 

 and Millipedes (Myriapoda\ and the true Insects (Insecta). 

 The latter comprises the Spoon-worms (Gephyrea), the Leeches 

 (Hirudinea), the Earth-worms (Oligocfuzta}, the Tube-worms 

 ( Tubicola), and the Sand-worms or Sea-worms (Errantid) ; the 

 last four groups constituting the class of the Ringed Worms or 

 Annelida. 



Regarded as a whole, the great Annulose sub-kingdom 

 seems to have commenced at least as early as the Echinoder- 

 mata and the Ccelenterata. Both the Anarthropodous and 

 Arthropodous divisions of the sub-kingdom are represented in 

 the Upper Cambrian ; and the former, at any rate, is repre- 

 sented in the Lower Cambrian period, along with the earliest 

 traces of life known to us, except the Eozob'n of the Laurentian 

 Series. 



ANNELIDA. 



In the Anarthropodous division of the Annulosa the loco- 

 motive appendages are never distinctly jointed or articulated 

 to the body ; and the integument, though usually capable of 

 secreting chitine or horny matter, is almost always quite soft 

 and flexible. The Spoon-worms (Gephyrea), and two orders 

 of the Annelides (viz., the Leeches and the Earth-worms), are 

 wholly unknown in the fossil condition, and need not be con- 

 sidered here. There remain only two orders of the Annelides 



