﻿450 
  Prof. 
  M'lntosh 
  on 
  the 
  

  

  inferior 
  and 
  external 
  to 
  the 
  ventral 
  longitudinal 
  muscle. 
  

   The 
  area 
  of 
  the 
  nerve 
  in 
  transverse 
  section 
  is 
  crossed 
  by 
  

   strong- 
  vertical 
  fibres 
  (probably 
  of 
  connective 
  tissue), 
  and 
  the 
  

   neural 
  canal 
  is 
  external, 
  its 
  compartment 
  being 
  separated 
  by 
  

   a 
  distinct 
  series 
  of 
  vertical 
  fibres 
  passing 
  from 
  the 
  chitinous 
  

   support 
  of 
  the 
  ventral 
  longitudinal 
  muscle 
  to 
  the 
  cuticle. 
  

   Then 
  the 
  canal 
  becomes 
  more 
  closely 
  related 
  to 
  the 
  nerve, 
  

   while 
  the 
  latter 
  moves 
  under 
  the 
  ventral 
  longitudinal 
  muscle. 
  

   As 
  soon 
  as 
  the 
  walls 
  of 
  the 
  body 
  are 
  more 
  completely 
  

   rounded 
  (in 
  section) 
  the 
  neural 
  canal 
  occurs 
  at 
  the 
  outer 
  

   and 
  inferior 
  border 
  of 
  the 
  nerve-area, 
  which 
  now 
  lies 
  

   under 
  the 
  raphe 
  to 
  which 
  the 
  vertical 
  and 
  oblique 
  muscles 
  

   are 
  attached. 
  Thereafter 
  the 
  neural 
  canal 
  glides 
  on 
  each 
  

   side 
  to 
  the 
  inner 
  and 
  inferior 
  border 
  of 
  the 
  nerve 
  and 
  its 
  

   calibre 
  is 
  considerably 
  increased. 
  Each 
  then 
  gets 
  wholly 
  

   below 
  the 
  nerve, 
  the 
  most 
  conspicuous 
  vertical 
  fibrous 
  band 
  

   being 
  external. 
  Within 
  is 
  a 
  fine 
  chitinous-like 
  membrane, 
  

   which 
  does 
  not 
  form 
  a 
  very 
  contractile 
  lining, 
  though 
  the 
  

   action 
  of 
  the 
  fibres 
  around 
  it 
  may 
  assist 
  in 
  this 
  respeet. 
  

   The 
  canal 
  shows 
  no 
  current 
  of 
  fluid 
  in 
  the 
  living 
  form, 
  and 
  all 
  

   that 
  can 
  be 
  said 
  of 
  it 
  in 
  the 
  preparations 
  is 
  that 
  it 
  sometimes 
  

   contains 
  a 
  translucent 
  gelatinous 
  substance. 
  The 
  nerves 
  

   and 
  neural 
  canals 
  preserve 
  the 
  foregoing 
  relations 
  till 
  they 
  

   reach 
  the 
  region 
  in 
  front 
  of 
  the 
  seventh 
  pair 
  of 
  bristle-bundles, 
  

   where 
  the 
  canals 
  leave 
  the 
  nerve-trunks, 
  pass 
  inward 
  under 
  

   the 
  short 
  transverse 
  muscle, 
  and 
  unite 
  in 
  the 
  middle 
  line 
  to 
  

   form 
  a 
  single 
  large 
  canal, 
  which 
  thus 
  lies 
  between 
  the 
  nerves 
  

   and 
  separated 
  from 
  them 
  by 
  a 
  considerable 
  hypodermic 
  

   interval. 
  The 
  extreme 
  shortening 
  of 
  the 
  transverse 
  ventral 
  

   muscles 
  at 
  the 
  posterior 
  part 
  of 
  the 
  ninth 
  segment 
  permits 
  

   the 
  approximation 
  of 
  the 
  nerve-cords, 
  so 
  that 
  at 
  the 
  com- 
  

   mencement 
  of 
  the 
  median 
  ventral 
  blood-vessel 
  they 
  are 
  

   situated 
  at 
  each 
  side 
  of 
  the 
  large 
  neural 
  canal, 
  and 
  soon 
  (in 
  

   the 
  same 
  segment) 
  insinuate 
  themselves 
  above 
  it. 
  This 
  

   arrangement 
  continues 
  to 
  the 
  posterior 
  part 
  of 
  the 
  body, 
  

   but 
  toward 
  the 
  tip 
  of 
  the 
  tail 
  the 
  nerves 
  form 
  a 
  single 
  

   (united) 
  cord 
  ; 
  while 
  the 
  neural 
  canal 
  (which 
  in 
  the 
  ordinary 
  

   sections 
  forms 
  a 
  large 
  transversely 
  flattened 
  channel, 
  like 
  

   that 
  of 
  a 
  non-contractile 
  vessel) 
  diminishes 
  and 
  disappears. 
  

  

  A 
  series 
  of 
  fine 
  nerve-branches, 
  forming 
  a 
  plexus, 
  is 
  some- 
  

   times 
  observed 
  passing 
  out 
  to 
  the 
  lateral 
  organs. 
  The 
  twigs 
  

   run 
  in 
  a 
  parallel 
  manner 
  at 
  first, 
  then 
  diverge, 
  their 
  fine 
  

   branches 
  anastomosing 
  in 
  various 
  directions. 
  

  

  