ANNELIDA. 309 



Arthropodous divisions of the sub-kingdom are represented 

 in the Upper Cambrian; and the former, at any rate, is 

 represented in the Lower Cambrian period, along with the 

 earliest traces of life known to us, except the Eozoon 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), the Arrow- worms 

 (Chcetognatka), and two orders of the Annelides (viz., the 

 Leeches and the Earth-worms), are wholly unknown in the 

 fossil condition, and need not be considered here. There 

 remain only two orders of the Annelides (viz., the Tube- 

 worms or Tubicola, and the Sand-worms or Errantia} which 

 come under the observation of the palaeontologist, and neither 

 of these requires much notice. In both orders, as through- 

 out the division, the integument is more or less soft, and 

 there are no internal hard structures, except, occasionally, 

 horny jaws ; hence it is doubtful if we have any example 

 of the fossilised body of these creatures, though such have 

 been alleged to occur. The Tubicolous Annelides, however, 

 protect themselves by a tube of lime, sand, or adventitious 

 particles, and these investing tubes are often preserved in 

 the fossil condition. The Errant Annelides, again, besides 

 their fossilised jaws, have left numerous traces of their past 

 existence in the form of filled-up burrows or meandering trails 

 upon the soft sand and mud of the sea-bottom ; and from 

 these we know that the Annelides commenced their existence 

 at least as early as the Lower Cambrian period, obscure traces 

 of their presence having been even detected in the Lauren- 

 tian Series. 



ORDER TUBICOLA. The Tubicolous Annelides are distin- 

 guished by the fact that the body is protected by a tube, within 

 which the animal can withdraw itself by means of tufts of 

 bristles carried on the sides of the body. The gills are placed 



