446 



ZOOLOGY 



SECT. 



' situated in the bases of the parapodia. A delicate longitudinal 

 I 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 



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

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



oi 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 oesophageal 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 



