NERVOUS SYSTEM. INVERTEBRATA. 11 



brain. The ganglia of the ventral chain are transversely 

 concentrated and show no external sign of their paired 

 nature ; they are metamerically disposed and united to one 

 another by a pair of closely approximated connectives. 

 Each ganglion gives off three pairs of nerves, the largest 

 of which arises furthest back and innervates the parapodia, 

 while the two anterior pairs supply the trunk muscles and 

 skin of the segment in which the ganglion lies. All parts 

 of the ventral chain are enclosed in a thick fibrous neuri- 

 lernma (subcuticular fibrous tissue), on the outer surface 

 of which there is a delicate homogeneous membrane (fig. 7). 



- H.M. 



C.M. 



Part of a Ventral-chcain Ganglion of Aphrodite aculeata in transverse 

 section. X 150. 



C.M. Central medulla. G.C. Ganglion-cells. H.M. Homogeneous 

 membrane. N.L. Neurilemma. S.F. Supporting fibres. 



Many delicate fibres derived from the neurilemma traverse 

 the substance of the connectives and ganglia. Ganglion- 

 cells are confined to the ventral surface of the ganglia; 

 they are lodged in the meshes of the neurilemma. 



In the upper specimen the anterior portion of the nervous 

 system including the brain and 7 ventral chain ganglia is 

 shown in an isolated condition. Below is an entire animal 

 in which the nervous system is displayed in situ by the 

 removal of the ventral body-walls from the mid-line. 



Rohde, Zool. Beitr., Bd. ii. 1890, p. 1. 



