﻿Structure 
  of 
  Magelona. 
  425 
  

  

  wedge 
  in 
  the 
  middle 
  line, 
  and 
  a 
  slightly 
  broader 
  region 
  at 
  

   the 
  sides 
  where 
  it 
  joins 
  the 
  lamellae. 
  The 
  lateral 
  wall 
  has 
  a 
  

   better 
  marked, 
  and 
  in 
  the 
  preparations 
  a 
  loosely 
  cellular, 
  

   belt 
  (due 
  to 
  the 
  escape 
  of 
  the 
  bacillary 
  corpuscles), 
  while 
  

   the 
  ventral 
  is 
  denser 
  and 
  somewhat 
  broader. 
  The 
  nerves 
  

   have 
  now 
  come 
  so 
  close 
  together 
  that 
  the 
  neural 
  canal 
  is 
  

   thrust 
  beneath 
  them. 
  The 
  fibres 
  of 
  the 
  hypoderm 
  slant 
  

   downward 
  and 
  inward 
  beneath 
  the 
  neural 
  canal 
  on 
  each 
  side 
  

   in 
  contraction. 
  The 
  cuticle 
  is 
  very 
  thin 
  over 
  the 
  lateral 
  

   regions, 
  somewhat 
  thicker 
  on 
  the 
  dorsal 
  aspect, 
  and 
  compa- 
  

   ratively 
  dense 
  over 
  the 
  nerve-area. 
  

  

  Toward 
  the 
  posterior 
  end 
  this 
  coat 
  forms 
  a 
  very 
  thin 
  layer 
  

   over 
  the 
  dorsal 
  and 
  ventral 
  longitudinal 
  muscles, 
  widening 
  

   at 
  the 
  outer 
  edge 
  of 
  each 
  to 
  join 
  the 
  thicker 
  lateral 
  hypoderm 
  

   in 
  which 
  bacillary 
  cells 
  abound. 
  On 
  each 
  side 
  of 
  the 
  sub- 
  

   neural 
  canal 
  there 
  is 
  an 
  increase 
  in 
  breadth, 
  but 
  the 
  median 
  

   dorsal 
  wedge 
  is 
  insignificant. 
  Near 
  the 
  tip 
  of 
  the 
  tail, 
  

   again, 
  the 
  neural 
  hypoderm 
  is 
  somewhat 
  larger 
  and 
  passes 
  

   further 
  outward 
  ; 
  that 
  on 
  the 
  lateral 
  regions 
  also 
  stretches 
  

   further 
  upward 
  and 
  downward, 
  and 
  abounds 
  in 
  large 
  bacillary 
  

   cells. 
  The 
  neural 
  canal 
  disappears 
  toward 
  the 
  tip 
  of 
  the 
  

   tail. 
  

  

  The 
  tapering 
  tail 
  ends 
  in 
  an 
  intermediate 
  rounded 
  portion 
  

   and 
  two 
  lateral 
  cirri, 
  as 
  in 
  certain 
  other 
  members 
  of 
  the 
  

   Spionidae. 
  Each 
  of 
  the 
  latter 
  processes 
  has 
  a 
  thin 
  covering 
  

   of 
  cuticle, 
  the 
  rest 
  being 
  hypodermic 
  tissue, 
  the 
  cells 
  or 
  

   glands 
  being 
  arranged 
  in 
  a 
  somewhat 
  regular 
  manner, 
  espe- 
  

   cially 
  along 
  the 
  posterior 
  border, 
  where 
  they 
  pass 
  from 
  the 
  

   cnticle 
  downward 
  and 
  inward. 
  The 
  cells 
  are 
  flask-shaped 
  or 
  

   fusiform 
  and 
  contain 
  granules 
  and 
  bacilli. 
  The 
  hypoderm 
  

   of 
  the 
  cirri 
  blends 
  smoothly 
  into 
  the 
  rounded 
  intermediate 
  

   portion. 
  

  

  The 
  description 
  of 
  the 
  lateral 
  lamellae 
  (which 
  are 
  two 
  on 
  

   each 
  side) 
  falls 
  under 
  this 
  head. 
  Each 
  of 
  these 
  (to 
  take, 
  for 
  

   example, 
  the 
  fourth 
  or 
  fifth 
  behind 
  the 
  ninth 
  bristle-bundles) 
  

   has 
  a 
  delicate 
  cuticular 
  investment, 
  the 
  interior 
  beiuo- 
  

   formed 
  by 
  hypodermic 
  tissue. 
  At 
  the 
  base 
  of 
  the 
  lamella 
  

   is 
  a 
  group 
  of 
  simple 
  bristles 
  (formerly 
  mentioned) 
  which 
  

   apparently 
  serves 
  to 
  strengthen 
  the 
  pedicle. 
  In 
  certain 
  views 
  

   a 
  channel 
  appears 
  in 
  the 
  latter, 
  but 
  no 
  fluid 
  has 
  been 
  seen 
  

   therein, 
  neither 
  is 
  there 
  a 
  vascular 
  coil 
  in 
  the 
  process. 
  

   During 
  life 
  considerable 
  contractions 
  occur 
  on 
  the 
  concave 
  

   side, 
  where 
  the 
  striated 
  muscular 
  fibres 
  lying 
  within 
  the 
  

   curve 
  of 
  the 
  bristles 
  of 
  the 
  process 
  pass 
  from 
  the 
  inferior 
  

   margin 
  of 
  the 
  upper 
  lamella 
  to 
  the 
  body-wall, 
  and 
  then 
  turn 
  

   outward 
  to 
  the 
  upper 
  border 
  of 
  the 
  inferior 
  process. 
  

  

  