﻿Structure 
  of 
  Magelona. 
  431 
  

  

  at 
  first 
  appears 
  iu 
  trausverse 
  section 
  as 
  a 
  small 
  band, 
  lying 
  

   chiefly 
  below 
  the 
  median 
  muscle, 
  and 
  having 
  the 
  vascular 
  

   area 
  superiorly 
  and 
  externally. 
  When 
  the 
  crown-shaped 
  

   arrangement 
  of 
  the 
  central 
  muscles 
  occurs, 
  the 
  external 
  (or 
  

   lateral) 
  have 
  attained 
  a 
  somewhat 
  larger 
  size, 
  and 
  their 
  fine 
  

   parallel 
  fasciculi 
  in 
  section 
  are 
  placed 
  in 
  a 
  concentric 
  

   manner 
  round 
  the 
  chitinous 
  loop. 
  Each 
  muscle 
  therefore 
  

   forms 
  a 
  hollow 
  process 
  in 
  the 
  snout, 
  and 
  in 
  the 
  fresh 
  

   specimen, 
  under 
  compression, 
  granules 
  and 
  cells 
  rush 
  to 
  and 
  

   fro 
  in 
  the 
  median 
  space. 
  The 
  latter, 
  in 
  the 
  preparations, 
  

   holds 
  lax 
  cellulo-granular 
  tissue 
  — 
  also 
  somewhat 
  concentri- 
  

   cally 
  arranged. 
  The 
  septum 
  between 
  it 
  and 
  the 
  median 
  

   muscle 
  is, 
  for 
  the 
  most 
  part, 
  occupied 
  by 
  the 
  vascular 
  area 
  

   and 
  presents 
  no 
  fasciculi, 
  so 
  that 
  the 
  muscle 
  thus 
  has 
  the 
  

   form 
  of 
  the 
  letter 
  U, 
  the 
  thickest 
  mass 
  occurring 
  superiorly, 
  

   and 
  the 
  thinnest 
  at 
  the 
  curve 
  of 
  the 
  U 
  externally. 
  At 
  the 
  

   tip 
  of 
  the 
  U 
  superiorly 
  the 
  fasciculi 
  are 
  directed 
  downward 
  

   and 
  outward, 
  and 
  inferiorly 
  upward 
  and 
  more 
  obliquely 
  

   outward. 
  Proceeding 
  backward 
  the 
  area 
  of 
  the 
  muscle 
  

   largely 
  increases, 
  chiefly 
  toward 
  the 
  ventral 
  surface, 
  but 
  the 
  

   general 
  direction 
  of 
  its 
  fasciculi 
  is 
  the 
  same. 
  Before 
  the 
  

   separation 
  of 
  the 
  muscles 
  in 
  front 
  of 
  the 
  mouth 
  the 
  area, 
  

   again, 
  considerably 
  diminishes, 
  especially 
  in 
  regard 
  to 
  the 
  

   lax 
  central 
  tissue. 
  Immediately 
  after 
  the 
  separation, 
  the 
  

   gap 
  caused 
  by 
  the 
  passage 
  of 
  the 
  vessels 
  under 
  the 
  central 
  

   area 
  is 
  filled 
  by 
  the 
  latter 
  tissue, 
  and 
  the 
  limbs 
  of 
  the 
  U 
  

   approach 
  each 
  other 
  more 
  closely 
  at 
  the 
  tip, 
  but 
  they 
  do 
  not 
  

   unite. 
  In 
  a 
  line 
  with 
  the 
  base 
  of 
  the 
  tentacles 
  the 
  small 
  

   rounded 
  area 
  of 
  each 
  lateral 
  muscle 
  in 
  section 
  is 
  almost 
  

   entirely 
  occupied 
  by 
  the 
  fasciculi, 
  which 
  are 
  nearly 
  horizontal 
  

   in 
  direction, 
  the 
  upper, 
  however, 
  inclining 
  downward 
  and 
  

   the 
  inferior 
  upward. 
  There 
  is 
  now 
  a 
  tendency 
  toward 
  a 
  

   ventral 
  position, 
  the 
  superior 
  curve 
  of 
  the 
  muscle 
  disappearing 
  

   and 
  the 
  inner 
  ventral 
  region 
  increasing 
  in 
  size. 
  Behind 
  the 
  

   tentacles 
  it 
  is 
  almost 
  vertical, 
  with 
  the 
  fasciculi 
  for 
  the 
  most 
  

   part 
  directed 
  transversely, 
  the 
  convex 
  chitinous 
  support 
  

   being 
  external 
  — 
  its 
  superior 
  edge 
  running 
  into 
  the 
  base- 
  

   ment-tissue 
  under 
  the 
  dorsal 
  hypoderm 
  ; 
  while 
  the 
  inferior 
  

   border 
  terminates 
  at 
  the 
  insertion 
  of 
  the 
  oblique 
  muscle 
  (in 
  

   this 
  region 
  vertical) 
  which 
  forms 
  its 
  inner 
  border 
  and 
  shuts 
  

   it 
  in 
  a 
  special 
  compartment. 
  In 
  the 
  concavity 
  of 
  the 
  

   muscle 
  is 
  still 
  found 
  a 
  little 
  of 
  the 
  lax 
  cellulo-granular 
  tissue. 
  

   The 
  muscle 
  gradually 
  enlarges 
  and 
  moves 
  downward 
  so 
  as 
  to 
  

   get 
  beneath 
  the 
  bristles 
  and 
  toward 
  the 
  infero-lateral 
  region. 
  

   About 
  the 
  ninth 
  body-segment 
  it 
  becomes 
  chiefly 
  ventral 
  

   in 
  position, 
  then 
  rapidly 
  diminishes 
  in 
  size 
  at 
  tins 
  segment, 
  

  

  