﻿444 
  Prof. 
  M'lntosli 
  on 
  the 
  

  

  intervals, 
  during 
  the 
  boring 
  operations 
  of 
  the 
  animal, 
  as 
  a 
  

   pinkish 
  distensible 
  sac, 
  which, 
  especially 
  in 
  partial 
  extrusion, 
  

   often 
  presents 
  a 
  most 
  regularly 
  rugose 
  appearance. 
  In 
  

   complete 
  expulsion 
  the 
  general 
  form 
  is 
  that 
  of 
  a 
  reddish 
  

   apple 
  marked 
  with 
  flattened 
  ribs, 
  which 
  run 
  from 
  the 
  deep 
  

   dimple 
  at 
  the 
  apex 
  to 
  the 
  base. 
  At 
  the 
  upper 
  part 
  of 
  the 
  

   protruded 
  organ 
  is 
  a 
  somewhat 
  elongated 
  conical 
  smooth 
  

   portion, 
  marked 
  only 
  by 
  the 
  fine 
  longitudinal 
  lines 
  of 
  the 
  

   retractor 
  muscle 
  and 
  not 
  by 
  ribs. 
  The 
  blood 
  chiefly 
  occupies 
  

   the 
  upper 
  and 
  middle 
  regions, 
  but 
  this 
  is 
  due 
  to 
  position, 
  

   since 
  there 
  is 
  no 
  reason 
  why 
  it 
  should 
  not 
  enter 
  any 
  hollow 
  

   portion 
  of 
  the 
  extruded 
  organ. 
  Within 
  the 
  body 
  of 
  the 
  

   animal 
  it 
  forms 
  a 
  longitudinally 
  folded 
  sac 
  continuous 
  

   anteriorly 
  with 
  the 
  great 
  transverse 
  inferior 
  lip, 
  and 
  placed 
  

   along 
  the 
  ventral 
  region 
  of 
  the 
  body-cavity, 
  below 
  the 
  

   digestive 
  system. 
  Posteriorly 
  it 
  ends 
  in 
  a 
  cut 
  de 
  sac, 
  to 
  the 
  

   sides 
  and 
  termination 
  of 
  which 
  the 
  great 
  muscular 
  retractor 
  

   is 
  attached. 
  The 
  upper 
  and 
  anterior 
  fold, 
  again, 
  is 
  con- 
  

   tinuous 
  with 
  the 
  buccal 
  mucous 
  surface, 
  so 
  that 
  in 
  extrusion 
  

   an 
  uninterrupted 
  rim 
  is 
  found 
  at 
  the 
  sides, 
  while 
  the 
  centre 
  

   of 
  the 
  alimentary 
  canal 
  is 
  blocked 
  by 
  the 
  outward 
  folds 
  of 
  

   the 
  pharynx, 
  the 
  protrusion 
  of 
  the 
  proboscis 
  being 
  thus 
  

   inimical 
  to 
  swallowing; 
  indeed 
  the 
  functions 
  of 
  the 
  organ 
  

   are 
  not 
  digestive. 
  

  

  In 
  partial 
  protrusion 
  the 
  proboscis 
  under 
  pressure 
  presents 
  

   a 
  series 
  of 
  somewhat 
  radiated 
  lines 
  — 
  due 
  to 
  the 
  prominent 
  

   chitinous 
  folds 
  of 
  its 
  lining 
  membrane, 
  in 
  which 
  no 
  pores 
  

   have 
  been 
  made 
  out. 
  The 
  fibres 
  of 
  the 
  short 
  and 
  long 
  

   retractors 
  spread 
  out 
  in 
  the 
  central 
  region, 
  and 
  the 
  organ 
  is 
  

   crossed 
  by 
  the 
  fibres 
  of 
  the 
  circular 
  coat. 
  The 
  fibres 
  of 
  the 
  

   short 
  retractors, 
  which 
  pass 
  from 
  the 
  dorsal 
  raphe 
  on 
  each 
  

   side 
  of 
  the 
  body-wall, 
  expand 
  in 
  a 
  fan-like 
  manner, 
  chiefly 
  

   at 
  the 
  basal 
  part 
  of 
  the 
  extruded 
  organ, 
  and 
  therefore 
  in 
  the 
  

   retracted 
  condition 
  are 
  connected 
  with 
  its 
  anterior 
  region 
  ; 
  

   while 
  the 
  fibres 
  of 
  the 
  long 
  retractor 
  spread 
  over 
  a 
  wider 
  

   area, 
  for 
  the 
  most 
  part 
  toward 
  the 
  outer 
  part 
  of 
  the 
  organ 
  

   in 
  protrusion, 
  and 
  thus 
  in 
  retraction 
  are 
  attached 
  to 
  the 
  

   posterior 
  region. 
  In 
  extreme 
  protrusion 
  it 
  forms 
  a 
  large 
  

   flattened 
  bag, 
  which 
  does 
  not 
  quite 
  reach 
  the 
  tip 
  of 
  the 
  

   snout. 
  Externally, 
  and 
  especially 
  at 
  the 
  tip 
  in 
  extrusion, 
  is 
  

   the 
  dense 
  chitinous 
  coat, 
  continuous 
  with 
  that 
  of 
  the 
  mouth 
  

   superiorly, 
  and 
  with 
  the 
  cuticle 
  at 
  the 
  transverse 
  fold 
  or 
  

   lower 
  lip 
  inferiorly 
  : 
  beneath 
  is 
  a 
  streaked 
  granular 
  layer 
  

   homologous 
  with 
  the 
  hypoderm 
  of 
  the 
  body-wall; 
  indeed, 
  

   continuous 
  with 
  it. 
  In 
  partial 
  protrusion 
  this 
  coat 
  follows 
  

   the 
  previous 
  in 
  forming 
  numerous 
  elevated 
  ridges 
  and 
  folds 
  — 
  

  

  