﻿424 
  Prof. 
  M'Intosh 
  on 
  the 
  

  

  over 
  the 
  longitudinal 
  ventral 
  muscle 
  — 
  on 
  the 
  ventral 
  surface 
  

   of 
  which 
  it 
  increases 
  in 
  depth, 
  — 
  to 
  protect 
  the 
  nerve-trunk 
  

   situated 
  in 
  the 
  hollow 
  next 
  the 
  oblique 
  muscle. 
  The 
  layer 
  

   then 
  gradually 
  diminishes 
  toward 
  the 
  middle 
  line, 
  and, 
  

   passing 
  over, 
  follows 
  the 
  same 
  arrangement 
  on 
  the 
  opposite 
  

   side. 
  The 
  neural 
  canal 
  now 
  lies 
  on 
  the 
  ventral 
  aspect 
  of 
  the 
  

   nerve-trunk. 
  The 
  thick 
  layer 
  on 
  the 
  lateral 
  dorsal 
  regions 
  

   has 
  the 
  hypodermic 
  fibres 
  directed 
  upward 
  and 
  outward, 
  

   while 
  the 
  fibres 
  in 
  the 
  ventral 
  masses 
  at 
  the 
  nerve-trunks 
  

   pass 
  outward 
  and 
  downward. 
  The 
  hypodermic 
  nerve-area 
  

   soon 
  becomes 
  quite 
  ventral 
  in 
  position, 
  and 
  the 
  neural 
  canal 
  

   is 
  inferior 
  and 
  internal 
  to 
  the 
  nerve. 
  The 
  latter 
  is 
  further 
  

   protected 
  by 
  a 
  thicker 
  layer 
  of 
  cuticle 
  than 
  that 
  on 
  the 
  

   dorsum. 
  Just 
  below 
  the 
  inferior 
  bristle-buodles 
  (at 
  the 
  

   lower 
  edge 
  of 
  the 
  attachment 
  of 
  the 
  oblique 
  muscle) 
  a 
  rather 
  

   constant 
  fold 
  of 
  the 
  hypoderm 
  and 
  cuticle 
  occurs 
  from 
  the 
  

   fourth 
  to 
  about 
  the 
  eighth 
  segment, 
  and 
  in 
  transverse 
  sections 
  

   a 
  space 
  (or 
  canal) 
  appears 
  in 
  the 
  hypoderm. 
  The 
  granular 
  

   matter 
  next 
  the 
  basement-tissue 
  is 
  also 
  increased 
  at 
  this 
  

   point. 
  

  

  The 
  chief 
  change 
  that 
  ensues 
  in 
  the 
  anterior 
  region 
  of 
  the 
  

   body 
  is 
  the 
  gradual 
  diminution 
  of 
  the 
  hypodermic 
  area 
  

   between 
  the 
  nerve-cords. 
  The 
  neural 
  canals, 
  leaving 
  the 
  

   latter, 
  glide 
  inward 
  to 
  the 
  middle 
  line, 
  first 
  getting 
  under 
  

   the 
  convex 
  bellies 
  of 
  the 
  transverse 
  muscles 
  and 
  then 
  uniting 
  

   in 
  the 
  centre. 
  The 
  nerves 
  still 
  occupy 
  a 
  position 
  on 
  each 
  

   side 
  under 
  the 
  point 
  of 
  attachment 
  of 
  the 
  vertical 
  and 
  oblique 
  

   muscles. 
  In 
  regard 
  to 
  the 
  disposition 
  of 
  the 
  other 
  parts 
  

   of 
  the 
  hypoderm 
  it 
  may 
  be 
  mentioned 
  that 
  besides 
  the 
  

   increase 
  at 
  the 
  nerve-cords, 
  other 
  thickenings 
  occur 
  at 
  the 
  

   opposite 
  points 
  of 
  the 
  dorsal 
  region 
  in 
  the 
  preparations 
  (viz. 
  

   at 
  the 
  dorsal 
  end 
  of 
  the 
  vertical 
  muscular 
  band). 
  The 
  

   shortening 
  and 
  diminution 
  of 
  the 
  transverse 
  ventral 
  muscle 
  

   toward 
  the 
  posterior 
  end 
  of 
  the 
  region 
  permit 
  the 
  nerve-cords 
  

   to 
  approach 
  each 
  other 
  ; 
  indeed, 
  little 
  hypoderm 
  is 
  left 
  

   between 
  them 
  around 
  the 
  median 
  (neural) 
  caual. 
  In 
  the 
  

   ninth 
  segment 
  the 
  dorsal 
  hypoderm 
  is 
  divided 
  into 
  a 
  narrow 
  

   layer 
  over 
  the 
  muscles 
  and 
  the 
  two 
  great 
  dorsal 
  lamella?. 
  

   That 
  on 
  the 
  lateral 
  wall 
  of 
  the 
  body 
  has 
  diminished 
  in 
  

   depth, 
  but 
  the 
  ventral 
  hypoderm 
  is 
  not 
  much 
  altered. 
  Then 
  

   the 
  great 
  infero-lateral 
  lamellae 
  occupy 
  the 
  body-wall, 
  and 
  

   confine 
  the 
  ventral 
  hypoderm 
  to 
  a 
  narrower 
  area. 
  Finally, 
  

   the 
  dorsal 
  layer 
  diminishes 
  in 
  thickness 
  and 
  spreads 
  outward, 
  

   so 
  as 
  to 
  inaugurate 
  the 
  condition 
  of 
  the 
  posterior 
  region, 
  

   which 
  consists 
  of 
  a 
  very 
  thin 
  firm 
  granular 
  layer 
  of 
  hypo- 
  

   derm 
  over 
  the 
  dorsal 
  longitudinal 
  muscles, 
  with 
  a 
  deeper 
  

  

  