58 . INVERTEBRATE ANIMALS. "^ 



Group 157.— ANNELIDA ABKANCHIATA. Worms un- 

 provided with external organs of respiration. 



I. Order Hirudinea = Discophora. Aquatic worms 

 without lateral appendages of any kind, but having a 

 sucking disk posteriorly or at both extremities. Ten 

 genera are included, the forms " best known being the 

 Black-leech, the Horse-leech, and two species of the 

 common or medicinal Leech usually imported from 

 Hungary. The latter have ten minute eyes arranged 

 in the form of a horse-shoe over the upper part of the 

 anterior sucker. 



II. Order Oligoch^ta. Earth-worms, Lumhricidce, 

 possessing eight rows of short bristles acting as loco- 

 motive organs. The animals are eyeless, and have a 

 mouth without appendages. Water-worms, NdididcB, 

 including Tuhifex, a little bright-red worm inhabiting 

 the mud of impure streams. 



HI. Order Gephyrea. ys<pupa, a bridge ; often 

 regarded as a Class, but recognised by Mr. Huxley 

 as a division of inferior rank. The animals have affinity 

 with the Holothurians, a fact to which the name may 

 possibly allude, if it does not rather refer to the long 

 strangulated neck of the Spoon-worms, Sipunculidce, 

 frequently found on British coasts burrowing in the 

 sand or inhabiting the deserted shells of Whelks. 



Group 158.— ANNELIDA BRANCHIATA. Worms pro- 

 vided with external gills in the form of respiratory 

 tufts or plumes. 



I. Order Tubicola. In this Order the gills are 

 placed near the head of the animal, forming plumes 

 often of extreme beauty in colour and disposition. The 

 tube may be calcareous as in the little Spirorhis abun- 



