SEA MUSSEL MYTILUS EDULIS. 



175 



The osphradia are pigmented organs of dark brown color which lie ventral and 

 lateral to the visceral ganglia (fig. 169, Os, p. 178). They extend as far as the inner side 

 of the gill supports, each one covering an area about equal to that of the visceral 

 ganglion. 



163 



Fig. 163.— Diagrammatic representation of the nervous system of Myiilus edulis. 



A PN, anterior pallial nerve. 



.4 RN, anterior renal nerve. 



ASO, abdominal sense organ. 



BrN, branchial nerve. 



BuN, buccal nerve. 



CC, cerebral commissure. 



CG t cerebral ganglia. 



CPC, cerebropedal commissure. 



CVC, cere bro visceral commissure. 



DPN, dorsal pallial nerve. 



DRBN, dorsal retractor byssus nerve. 



E, eye. 



OpN, optic nerve, 



Ot, otocyst. 



OtN, otocyst nerve. 



PA d, posterior adductor muscle. 



PAX , posterior adductor nerve. 



PdG, pedal ganglion. 



PdN, pedal nerve. 



PDPN, posterior dorsal pallial nerve, 



PPdN, posterior pedal nerve. 



PRN, posterior renal nerve. 



PVPN, posterior ventral pallial nerve. 



SN, syphonal nerve. 



VG, visceral ganglion. 



\'RBN, ventral retractor byssus nerve. 



The abdominal sense organs, first described by Thiele (1889) in Area, were found by 

 List (1902) to be present in some form or other in all species of the Mytilidae. In 

 Myiilus edulis they lie on the ventral posterior side of the posterior adductor muscle 

 just outside of the gill supports. A microscopic cross section of a mussel taken through 

 the oosterior adductor muscle just behind the visceral ganglion will show the relative 



