﻿434 
  Prof. 
  M'lutosh 
  on 
  the 
  

  

  the 
  ninth 
  body-segment 
  each 
  muscle 
  diminishes 
  to 
  an 
  

   irregularly 
  rounded 
  area 
  situated 
  over 
  the 
  dorsal 
  blood- 
  

   vessel, 
  the 
  two 
  muscles 
  in 
  the 
  preparations 
  being 
  about 
  as 
  

   broad 
  as 
  the 
  constricted 
  intestinal 
  canal 
  of 
  the 
  region. 
  Then 
  

   a 
  strong 
  series 
  of 
  oblique 
  fibres 
  appears 
  beneath, 
  and, 
  indeed, 
  

   they 
  are 
  circumscribed 
  by 
  muscles 
  all 
  round. 
  This 
  narrow 
  

   part 
  merges 
  into 
  the 
  greatly 
  increased 
  dorsal 
  longitudinal 
  

   muscles 
  of 
  the 
  next 
  segment. 
  Thereafter 
  the 
  two 
  large 
  

   muscles 
  are 
  at 
  first 
  separated 
  by 
  an 
  intermediate 
  hypo- 
  

   dermic 
  process, 
  which 
  passes 
  downward 
  to 
  the 
  apex 
  of 
  the 
  

   oblique 
  muscle 
  and 
  the 
  alimentary 
  and 
  vascular 
  systems 
  

   beneath; 
  then 
  a 
  simple 
  sulcus 
  is 
  left, 
  from 
  which 
  the 
  

   fasciculi 
  in 
  transverse 
  section 
  pass 
  off 
  in 
  a 
  pennate 
  manner. 
  

   The 
  latter 
  arrangement 
  forms 
  a 
  projecting 
  portion 
  which 
  

   impinges 
  on 
  the 
  septum 
  between 
  the 
  dorsal 
  blood-vessels. 
  

   The 
  fasciculi 
  of 
  the 
  other 
  parts 
  of 
  each 
  muscle 
  resemble 
  

   those 
  of 
  the 
  ventral. 
  By-and-by 
  the 
  median 
  pennate 
  region 
  

   becomes 
  very 
  distinct 
  and 
  regular, 
  though 
  less 
  separated 
  

   from 
  the 
  general 
  body 
  of 
  the 
  muscle. 
  In 
  the 
  centre 
  is 
  the 
  

   chitinous 
  septum, 
  which 
  is 
  attached 
  to 
  the 
  plate 
  between 
  

   the 
  dorsal 
  blood-vessels 
  ; 
  while 
  from 
  each 
  side 
  of 
  the 
  former 
  

   the 
  fasciculi 
  proceed 
  in 
  a 
  nearly 
  horizontal 
  manner, 
  except 
  

   at 
  the 
  looer 
  fourth, 
  where 
  they 
  incline 
  downward 
  like 
  a 
  

   brush, 
  and 
  their 
  fibres 
  become 
  more 
  evidently 
  striated. 
  The 
  

   pennate 
  arrangement 
  continues 
  toward 
  the 
  posterior 
  end, 
  

   near 
  which 
  the 
  fasciculi 
  are 
  deepest 
  next 
  the 
  middle 
  line 
  of 
  

   the 
  dorsum 
  ; 
  but 
  it 
  disappears 
  before 
  the 
  termination 
  of 
  the 
  

   muscle, 
  a 
  section 
  near 
  the 
  top 
  of 
  the 
  tail 
  presenting 
  a 
  simple 
  

   ovoid 
  appearance. 
  

  

  The 
  advent 
  of 
  the 
  mouth 
  ushers 
  in 
  considerable 
  changes, 
  

   which 
  may 
  be 
  taken 
  in 
  series 
  according 
  to 
  their 
  position 
  in 
  

   the 
  body-wall 
  from 
  before 
  backward 
  — 
  in 
  transverse 
  section. 
  

   In 
  the 
  dorsal 
  hypoderm 
  the 
  section 
  of 
  the 
  small 
  longitudinal 
  

   muscle 
  appears 
  on 
  each 
  side 
  of 
  the 
  middle 
  line, 
  resting 
  on 
  a 
  

   narrow 
  tiansverse 
  muscle 
  which 
  spreads 
  out 
  at 
  each 
  end 
  

   over 
  the 
  vascular 
  trunks 
  to 
  the 
  tentacle. 
  It 
  has 
  in 
  the 
  

   middle 
  line 
  inferiorly 
  a 
  central 
  projection 
  to 
  which 
  the 
  

   vertical 
  fibres 
  of 
  the 
  space 
  formerly 
  alluded 
  to 
  are 
  attached. 
  

   On 
  each 
  side 
  of 
  the 
  median 
  line, 
  beneath 
  the 
  transverse 
  

   muscle, 
  is 
  a 
  continuation 
  of 
  the 
  nerve-centre. 
  The 
  muscle 
  

   is 
  intimately 
  associated 
  with 
  the 
  functions 
  of 
  the 
  oral 
  and 
  

   post-oral 
  regions, 
  attaining 
  great 
  development 
  for 
  a 
  con- 
  

   siderable 
  distance, 
  and 
  then, 
  as 
  the 
  longitudinal 
  dorsal 
  

   increase 
  in 
  magnitude, 
  disappearing 
  from 
  the 
  central 
  region. 
  

   Just 
  over 
  the 
  origin 
  of 
  the 
  nerve-trunks 
  from 
  the 
  cephalic 
  

   mass, 
  the 
  muscle 
  forms 
  a 
  continuous 
  transverse 
  band, 
  

  

  