﻿436 
  Prof. 
  M'lntosli 
  on 
  the 
  

  

  dorsal 
  muscle 
  are 
  seen 
  from 
  the 
  anterior 
  border 
  of 
  the 
  

   mouth 
  to 
  a 
  little 
  behind 
  the 
  tentacular 
  bases. 
  Moreover, 
  

   a 
  thin 
  but 
  distinct 
  layer 
  of 
  circular 
  fibres 
  envelops 
  the 
  

   body-wall 
  — 
  after 
  its 
  complete 
  formation 
  — 
  beneath 
  the 
  hypo- 
  

   dermic 
  basement-tissue, 
  It 
  is 
  continuous 
  to 
  the 
  posterior 
  

   end 
  of 
  the 
  worm. 
  

  

  hi 
  the 
  space 
  occurring 
  on 
  each 
  side 
  of 
  the 
  mouth, 
  and 
  

   which 
  is 
  in 
  connection 
  with 
  the 
  great 
  vascular 
  chamber, 
  

   are 
  a 
  scries 
  of 
  vertical 
  muscular 
  fibres, 
  proceeding 
  from 
  the 
  

   dorsum 
  and 
  attached 
  in 
  the 
  first 
  instance 
  to 
  the 
  upper 
  border 
  

   of 
  the 
  buccal 
  mucous 
  tissue 
  1 
  . 
  They 
  occupy 
  the 
  region 
  

   between 
  tin- 
  longitudinal 
  ventral 
  muscle 
  and 
  the 
  latter, 
  and 
  

   probably 
  act 
  as 
  retractors 
  of 
  the 
  tissue. 
  The 
  librcs 
  soon 
  

   increase 
  in 
  strength, 
  and 
  occupy 
  the 
  whole 
  of 
  the 
  somewhat 
  

   triangular 
  area 
  between 
  tin- 
  longitudinal 
  muscle 
  laterally 
  

   and 
  a 
  line 
  drawn 
  from 
  its 
  inferior 
  curve 
  to 
  the 
  dorsal 
  median 
  

   line. 
  The 
  fan-shaped 
  mass 
  of 
  fibres 
  converges 
  to 
  pass 
  the 
  

   longitudinal 
  muscle, 
  but 
  being 
  connected 
  with 
  the 
  pro- 
  

   boscis 
  their 
  insertion 
  is 
  not 
  observed 
  so 
  readily 
  ; 
  though 
  in 
  

   extrusion 
  of 
  the 
  latter 
  organ 
  they 
  are 
  seen 
  to 
  bend 
  over 
  

   into 
  it 
  and 
  become 
  attached, 
  chiefly 
  at 
  the 
  external 
  aspect. 
  

   In 
  the 
  latter 
  condition 
  of 
  the 
  proboscis 
  the 
  fibres 
  anteriorly 
  

   assume, 
  for 
  the 
  most 
  part, 
  a 
  vertical 
  direction, 
  and, 
  as 
  it 
  were, 
  

   bound 
  laterally 
  the 
  great 
  mass 
  of 
  longitudinal 
  muscular 
  

   librcs 
  which 
  are 
  placed 
  next 
  the 
  inner 
  bolder 
  in 
  the 
  extruded 
  

   organ. 
  Then 
  (proceeding 
  backward) 
  it 
  is 
  noticed 
  that 
  some 
  

   of 
  tin- 
  outer 
  vertical 
  fibres, 
  which 
  pass 
  down 
  from 
  the 
  

   dorsum 
  close 
  by 
  the 
  ventral 
  longitudinal 
  muscle, 
  become 
  

   attached 
  to 
  the 
  chitinous 
  continuation 
  of 
  its 
  inferior 
  

   boundary, 
  and 
  thus 
  cease 
  to 
  extend 
  into 
  the 
  extruded 
  

   proboscis. 
  Further, 
  the 
  fan-shaped 
  mass 
  of 
  fibres 
  is 
  split 
  

   into 
  two 
  by 
  the 
  Intervention 
  of 
  the 
  blood-channel. 
  Many 
  

   of 
  the 
  fibres 
  still 
  pass 
  into 
  the 
  proboscis, 
  but 
  they 
  soon 
  cease 
  

   to 
  do 
  so, 
  and 
  are 
  fixed 
  to 
  the 
  chitinous 
  plate 
  above 
  mentioned, 
  

   in 
  company 
  with 
  the 
  great 
  transverse 
  ventral 
  muscle. 
  The 
  

   latter 
  is 
  attached 
  to 
  the 
  ventral 
  aspect 
  of 
  the 
  chitinous 
  base- 
  

   ment-tissue, 
  and 
  therefore 
  probably 
  acts 
  in 
  opposition 
  to 
  

   the 
  fan-shaped 
  vertical 
  series. 
  From 
  the 
  extensive 
  con- 
  

   nection 
  of 
  the 
  latter 
  with 
  the 
  dorsal 
  region, 
  and 
  the 
  strength 
  

   of 
  the 
  transverse 
  1 
  ventral 
  muscle, 
  almost 
  the 
  whole 
  body- 
  

   cavity 
  will 
  be 
  firmly 
  compressed 
  during 
  their 
  contraction 
  

   and 
  the 
  proboscis 
  expelled. 
  

  

  The 
  interposition 
  of 
  the 
  blood-channel 
  in 
  the 
  great 
  fan- 
  

   shaped 
  anterior 
  muscle 
  — 
  already 
  noticed 
  — 
  separates 
  it 
  into 
  

   a 
  vertical 
  and 
  an 
  oblique 
  division. 
  The 
  vertical 
  librcs 
  

   spring 
  from 
  the 
  common 
  origin 
  at 
  the 
  outer 
  border 
  of 
  the 
  

  

  