446 ZOOLOGY SECT. 



situated in the bases of the parapodia. A delicate longitudinal 

 neural vessel accompanies the nerve-cord. 



Nereis is devoid of any branchiae ; but there can be little doubt 

 that the lobes of the parapods with their rich blood-supply, and the 

 areas of integument occupied by plexuses of blood-vessels, subserve 

 the function of respiration. 



There is a well-developed nervous system (Fig. 352), which is 

 bilateral and metameric in its arrangement, like the other systems 



n- 



FIG. 352. Nereis. Anterior portion of nervous system, comprising the brain, the oesophageal 

 connectives, and the anterior part of the ventral nerve-cord. (After Quatrefages.) 



01 organs. Situated in the prostomium is a large bilobed mass 

 of nerve-matter containing numerous nerve-cells, the cerelral 

 ganglion or brain (c). This gives off tentacular nerves to the tentacles 

 and palpi, and two pairs of short thick optic nerves to the eyes. 

 Behind, two thick nerve-strands, the assophageal connectives (d), curve 

 round the mouth in the peristomium to meet on the ventral 

 aspect behind the mouth and below the pharynx. The oesopha- 

 geal connectives with the cerebral ganglion thus form a ring 

 around the anterior part of the enteric canal. From them are 



