336 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



tlie prostomium, with which they ultimately become 

 connected. Each nerve branches several times, and gives 

 rise to a large number of extremely fine fibres, which 

 terminate in the sensory cells with which the prostomium 

 is amply provided. It is the presence of these sensory 

 cells which renders the prostomium such an important 

 tactile organ. 



The second pair of nerves arising from -the cerebral 

 ganglia form continuations of the antero-lateral lobes of 

 the brain, which have already been described. They are 

 short, and pass directly to the lateral walls of the 

 prostomium and first segment. Here they branch, 

 forming a number of fine fibres which spread themselves 

 over and into the body wall of this region. The third pair 

 arise as branches of the peripharyngeal commissure, and 

 pass to the body wall of the first segment, where they also 

 branch (PI. II, figs. 7 and 8). 



The Ventral Nerve Cord originates at that point 

 where the two connectives arising from the cerebral 

 ganglia unite below the gut, having first encircled it. 

 The nerve cord is a ganglionated chain extending from the 

 second segment to the last segment of the body, and it 

 lies freely through all its length in the body cavity. It 

 is surrounded by a connective tissue sheath, from which, 

 at intervals, branches arise and pass to the body wall. 

 By this means the nerve cord is kept in position in the 

 body cavity. It is necessary to exercise care in 

 identifying nerves, for these branches of the connective 

 tissue sheath closely resemble the nerves in appearance, 

 though not, of course, in structure. 



The cord is also enclosed in a muscular sheath, 

 which, however, does not completely encircle it, but is 

 confined principally to the dorsal surface. The sheath 

 is very delicate, and is composed of a few muscle fibres 



