﻿440 
  Prof. 
  M'lntosh 
  on 
  the 
  

  

  swim 
  freely 
  in 
  the 
  water 
  in 
  a 
  wriggling 
  manner 
  ; 
  indeed, 
  

   when 
  fresh, 
  its 
  vivacity 
  is 
  remarkable. 
  

  

  III. 
  The 
  Digestive 
  System. 
  

  

  The 
  mouth 
  opens 
  at 
  the 
  base 
  of 
  the 
  flattened 
  snout 
  as 
  a 
  

   somewhat 
  triangular 
  or 
  T-shaped 
  slit 
  surrounded 
  by 
  lips 
  of 
  

   mucous 
  membrane, 
  and 
  situated 
  between 
  or 
  very 
  slightly 
  in 
  

   front 
  of 
  the 
  bases 
  of 
  the 
  tentacles. 
  The 
  anterior 
  lip 
  is 
  

   sinuous 
  but 
  complete, 
  while 
  inferiorly 
  is 
  a 
  wide 
  fissure 
  

   (bounded 
  laterally 
  by 
  prominent 
  margins) 
  which 
  runs 
  a 
  

   considerable 
  distance 
  backward. 
  The 
  lips 
  are 
  very 
  mobile, 
  

   and 
  in 
  life 
  frequently 
  expand 
  to 
  gulp 
  water, 
  a 
  feature 
  

   common 
  in 
  the 
  Spionidse, 
  but 
  of 
  importance, 
  in 
  relation 
  to 
  

   the 
  blood-channels 
  in 
  the 
  neighbourhood, 
  in 
  this 
  form. 
  

  

  The 
  alimentary 
  region 
  behind 
  the 
  mouth 
  is 
  somewhat 
  

   complex, 
  and 
  may 
  be 
  divided 
  into 
  pharynx, 
  proboscis, 
  

   oesophagus, 
  and 
  intestine. 
  In 
  using 
  these 
  terms, 
  however, 
  

   no 
  special 
  weight 
  is 
  placed 
  on 
  them, 
  though 
  it 
  is 
  probable 
  

   that 
  the 
  barred 
  region 
  of 
  the 
  pharynx 
  is 
  homologous 
  with 
  

   the 
  proventriculus 
  of 
  the 
  Syllidse 
  and 
  others; 
  while 
  the 
  

   oesophageal 
  division 
  may 
  consist 
  of 
  gullet 
  and 
  ventricule 
  

   combined. 
  In 
  the 
  retracted 
  condition 
  of 
  the 
  proboscis 
  the 
  

   general 
  arrangement 
  is 
  as 
  follows 
  : 
  — 
  The 
  buccal 
  leads 
  into 
  a 
  

   pharyngeal 
  division, 
  which 
  is 
  thrown 
  into 
  numerous 
  prominent 
  

   rugse, 
  especially 
  posteriorly, 
  and 
  it 
  is 
  further 
  characterized 
  by 
  

   the 
  muscularity 
  of 
  its 
  walls. 
  To 
  this 
  region 
  is 
  appended 
  the 
  

   protrusible 
  proboscis 
  in 
  a 
  manner 
  afterwards 
  to 
  be 
  explained. 
  

   Behind 
  the 
  pharyngeal 
  is 
  the 
  oesophageal 
  division, 
  which 
  

   continues 
  to 
  the 
  ninth 
  body-segment 
  and 
  terminates 
  in 
  the 
  

   intestinal 
  region 
  proper. 
  

  

  It 
  has 
  already 
  been 
  noticed 
  that 
  the 
  hypodermic 
  tissue 
  of 
  

   the 
  ventral 
  surface 
  of 
  the 
  snout 
  becomes 
  greatly 
  hyper- 
  

   trophied 
  in 
  the 
  median 
  region 
  throughout 
  a 
  considerable 
  area 
  

   in 
  front 
  of 
  the 
  mouth. 
  It 
  is 
  especially 
  deep 
  anterior 
  to 
  the 
  

   space 
  for 
  the 
  transverse 
  muscle, 
  and 
  at 
  the 
  space 
  may 
  fairly 
  

   be 
  said 
  to 
  assume 
  the 
  lax 
  translucent 
  character 
  distinctive 
  of 
  

   the 
  alimentary 
  modification. 
  In 
  longitudinal 
  sections 
  the 
  

   point 
  of 
  separation 
  is 
  recognized 
  by 
  the 
  thinness 
  of 
  the 
  

   cuticle. 
  Externally 
  is 
  a 
  distinct 
  layer 
  of 
  transparent 
  chiti- 
  

   nous 
  tissue 
  continuous 
  with, 
  though 
  much 
  thinner 
  than, 
  the 
  

   cuticle, 
  then 
  a 
  series 
  of 
  granular 
  and 
  rather 
  translucent 
  

   gland-cells 
  between 
  the 
  former 
  and 
  the 
  basement-tissue. 
  

   The 
  buccal 
  folds 
  occupy 
  a 
  large 
  area 
  in 
  protrusion 
  of 
  the 
  

   proboscis 
  at 
  the 
  point 
  of 
  separation 
  of 
  the 
  dorsal 
  transverse 
  

   muscle, 
  and 
  they 
  are 
  somewhat 
  symmetrically 
  arranged. 
  

  

  