﻿Structure 
  q/* 
  Miigelona. 
  439 
  

  

  shortly 
  fusiform 
  or 
  almost 
  baccate 
  in 
  contraction, 
  especially 
  

   toward 
  the 
  termination 
  of 
  the 
  region, 
  the 
  median 
  ventral 
  

   sulcus 
  being 
  very 
  deep. 
  At 
  the 
  ninth 
  body-segment 
  many 
  of 
  

   the 
  fibres, 
  as 
  formerly 
  noticed 
  in 
  connection 
  with 
  the 
  great 
  

   fan-shaped 
  muscle 
  of 
  the 
  part, 
  seem 
  to 
  pass 
  right 
  across 
  the 
  

   median 
  septum, 
  from 
  one 
  muscle 
  to 
  the 
  other. 
  They 
  

   diminish 
  much 
  immediately 
  thereafter, 
  so 
  that 
  at 
  the 
  com- 
  

   mencement 
  of 
  the 
  greenish 
  intestine 
  in 
  the 
  next 
  segment 
  

   only 
  their 
  form 
  is 
  indicated 
  by 
  two 
  small 
  swellings 
  on 
  the 
  

   band 
  between 
  the 
  longitudinal 
  ventral 
  muscles. 
  Finally, 
  

   the 
  chitinous 
  band 
  into 
  which 
  they 
  degenerate 
  separates 
  the 
  

   ventral 
  blood-vessel 
  from 
  the 
  nerve-cords, 
  and 
  externally 
  

   gives 
  attachment 
  to 
  the 
  vertical 
  and 
  oblique 
  muscles. 
  This 
  

   double-bellied 
  condition 
  of 
  the 
  atrophied 
  remnant 
  of 
  the 
  

   transverse 
  muscle 
  is 
  continued 
  to 
  the 
  posterior 
  end 
  of 
  the 
  

   worm 
  — 
  little 
  more 
  than 
  the 
  chitinous 
  tissue 
  (which 
  in 
  front 
  

   supported 
  the 
  muscle) 
  being 
  left. 
  

  

  The 
  muscular 
  arrangements 
  of 
  the 
  anterior 
  region 
  of 
  the 
  

   body 
  render 
  the 
  presence 
  of 
  dissepiments 
  unnecessary, 
  so 
  

   that 
  the 
  first 
  occurs 
  at 
  the 
  commencement 
  of 
  the 
  posterior 
  

   division, 
  and 
  they 
  are 
  continued 
  in 
  each 
  segment 
  to 
  the 
  tail. 
  

   Each 
  forms 
  a 
  muscular 
  screen 
  situated 
  a 
  short 
  distance 
  

   behind 
  the 
  lamellse 
  and 
  hooks, 
  and, 
  while 
  permitting 
  the 
  

   passage 
  of 
  the 
  perivisceral 
  fluid, 
  serves 
  to 
  support 
  the 
  

   intestine 
  and 
  the 
  blood-vessels. 
  

  

  The 
  bristle-muscles 
  are 
  on 
  the 
  whole 
  feebly 
  developed 
  and 
  

   somewhat 
  indistinct, 
  but 
  they 
  seem 
  to 
  agree 
  with 
  those 
  in 
  

   allied 
  forms. 
  The 
  roots 
  of 
  the 
  superior 
  bristles 
  of 
  the 
  

   anterior 
  region 
  pass 
  obliquely 
  inward 
  to 
  the 
  upper 
  part 
  of 
  

   the 
  vascular 
  space 
  between 
  the 
  vertical 
  and 
  oblique 
  muscles, 
  

   and 
  the 
  special 
  slips 
  radiate 
  outward 
  to 
  the 
  hypoderm. 
  The 
  

   roots 
  of 
  the 
  inferior, 
  again, 
  abut 
  on 
  the 
  upper 
  part 
  of 
  the 
  

   hollow 
  of 
  the 
  ventral 
  longitudinal 
  muscle. 
  Their 
  special 
  

   slips 
  follow 
  a 
  similar 
  arrangement. 
  Those 
  of 
  the 
  ninth 
  body- 
  

   segment 
  have 
  homologous 
  relations 
  with 
  surrounding 
  parts, 
  

   but 
  they 
  form 
  a 
  much 
  larger 
  fan-shaped 
  transverse 
  series, 
  

   the 
  diminution 
  of 
  the 
  dorsal 
  and 
  ventral 
  longitudinal 
  muscles 
  

   affording 
  ample 
  space 
  for 
  their 
  expansion. 
  In 
  the 
  posterior 
  

   region 
  of 
  the 
  body 
  the 
  great 
  increase 
  of 
  the 
  longitudinal 
  

   muscles 
  just 
  mentioned 
  causes 
  the 
  hooks 
  to 
  assume 
  a 
  more 
  

   or 
  less 
  vertical 
  position. 
  Their 
  muscles 
  are 
  similar 
  to 
  those 
  

   moving 
  the 
  anterior 
  bristles 
  ; 
  and 
  as 
  they 
  are 
  on 
  elevated 
  

   hypodermic 
  processes 
  continuous 
  with 
  the 
  lamellae, 
  both 
  are 
  

   probably 
  acted 
  on 
  thereby. 
  

  

  The 
  foregoing 
  muscular 
  system 
  enables 
  the 
  animal 
  to 
  

   perforate 
  the 
  moist 
  sand 
  with 
  great 
  rapidity, 
  as 
  well 
  as 
  to 
  

  

  