1 84 



ANIMALS 



This chain of ganglia lies on the ventral side, just on the inside 

 of the epidermis. The fibres of the sensory cells enter the 

 ganglia through the paired lateral nerves, which spring from 

 each ganglion and pass out to all parts of the corresponding 



FIG. 98. 



FIG. 99. 



FIG. 98. Diagram of the nervous system of nereis. A, The brain, ventral 

 nerve cord, and the five nerves of a metamere; B, diagram of a parapodium to 

 show the chief branches of nerve II. Br, Brain; C, circum-cesophageal con- 

 nectives; E, eye; N, nerves; Oe, oesophagus; Par, parapodium; P.gn, parapodial 

 ganglion; S.g., segmental ganglion; V.N., ventral nerve cord. 



FIG. 99. Diagram to show the relation of sensory fibres (S.F.), motor fibres 

 (M.F.) and association fibres (A.F.) in a simple type of central nervous system. 

 Ep, epidermis; Gl, ganglion; M , muscle; V.N.C., ventral nerve cord. 



segment. The ganglia contain two classes of cells: i. Those 

 which send fibres up and down the chain to other ganglia, but 

 do not pass out of the central system, and 2, those which send 

 fibres out to the other organs through the lateral nerves. In 



