﻿Structure 
  of 
  Magelona. 
  1 
  2 
  1 
  

  

  cuticle, 
  as 
  in 
  this 
  case, 
  often 
  coinciding 
  with 
  entire 
  absence 
  

   of 
  cilia). 
  Instead 
  of 
  that 
  disintegration 
  of 
  surface 
  which 
  so 
  

   readily 
  takes 
  place 
  in 
  the 
  latter, 
  it 
  is 
  often 
  found 
  that 
  the 
  

   tough 
  hyaline 
  cuticle 
  holds 
  together, 
  as 
  in 
  a 
  bag, 
  the 
  decaying 
  

  

  and 
  pulpy 
  internal 
  tissues. 
  In 
  this 
  form 
  the 
  cuticle 
  is 
  

   characterized 
  hy 
  its 
  great 
  strength 
  on 
  the 
  head 
  and 
  anterior 
  

   region 
  of 
  the 
  body, 
  so 
  as 
  to 
  enable 
  it 
  to 
  resist 
  the 
  friction 
  

   inseparable 
  from 
  such 
  active 
  habits 
  in 
  I 
  he 
  sand. 
  M. 
  Clapa- 
  

   rede 
  observes 
  that 
  tin; 
  sedentary 
  annelids 
  arc 
  characterized 
  

   by 
  the 
  delicacy 
  of 
  this 
  coat, 
  a 
  condition 
  Ik; 
  attributes 
  to 
  the 
  

   special 
  protection 
  afforded 
  by 
  their 
  tubes; 
  and 
  the 
  habits 
  of 
  

   Magelona 
  would 
  explain 
  the 
  structural 
  differences 
  in 
  this 
  

   respect 
  between 
  the 
  anterior 
  and 
  posterior 
  regions 
  of 
  the 
  

   body. 
  

  

  Tin; 
  habits 
  of 
  Magelona 
  seem 
  to 
  be 
  too 
  active 
  lor 
  the 
  

   attachment 
  of 
  external 
  parasites 
  (Infusoria 
  &c.) 
  which 
  are 
  

   common 
  in 
  Nephtkys 
  and 
  other 
  forms 
  that 
  burrow 
  in 
  the 
  

   sand. 
  

  

  2. 
  The 
  Hypoderm. 
  

  

  The 
  hypoderm 
  forms 
  a 
  very 
  large 
  proportion 
  of 
  the 
  tissues 
  

   of 
  the 
  flattened 
  snout 
  *, 
  the 
  whole 
  region 
  outside 
  the 
  four 
  

   muscular 
  compartments 
  being 
  occupied 
  by 
  it; 
  and 
  when 
  the 
  

   snout 
  attains 
  full 
  development 
  the 
  Lateral 
  hypodermic 
  expan- 
  

   sion 
  almost 
  equals 
  in 
  breadth 
  the 
  entire 
  muscular 
  region. 
  

   The 
  lateral 
  expansion 
  is 
  often 
  deeply 
  frilled 
  during 
  life, 
  and, 
  

   moreover, 
  presents 
  certain 
  secondary 
  folds 
  within 
  the 
  edge 
  — 
  

   features 
  which 
  would 
  lead 
  one 
  to 
  suppose 
  that 
  it 
  contains 
  no 
  

   muscular 
  fibres. 
  In 
  front 
  of 
  the 
  dilatation 
  at 
  the 
  origin 
  of 
  

   each 
  tentacle 
  a 
  semilunar 
  fold, 
  with 
  the 
  concavity 
  directed 
  

   outward, 
  occurs 
  at 
  the 
  margin. 
  The 
  hypoderm 
  also 
  forms 
  a 
  

   wedge-shaped 
  mass 
  between 
  the 
  median 
  muscular 
  compart- 
  

   ments 
  anteriorly. 
  After 
  the 
  muscular 
  chambers 
  are 
  fully 
  

   formed 
  the 
  snout 
  may 
  be 
  divided 
  into 
  a 
  median 
  and 
  two 
  

   lateral 
  regions, 
  though, 
  of 
  course, 
  the 
  tissue 
  is 
  quite 
  con- 
  

   tinuous. 
  The 
  dorsal 
  hypoderm 
  forms 
  an 
  almost 
  uniform 
  

   belt 
  of 
  cells 
  and 
  granules, 
  which, 
  in 
  vertical 
  transverse 
  

   section, 
  present 
  numerous 
  nearly 
  vertical 
  streaks. 
  The 
  

   breadth 
  of 
  the 
  ventral 
  hypoderm 
  is 
  greatest 
  toward 
  the 
  

   median 
  line, 
  diminishes 
  at 
  each 
  side 
  to 
  a 
  mere 
  streak 
  under 
  

   the 
  external 
  muscle, 
  and 
  again 
  expands 
  in 
  tin; 
  lateral 
  region. 
  

   The 
  symmetrical 
  streaks 
  of 
  the 
  median 
  part 
  (which 
  is 
  more 
  

  

  * 
  Ranzania, 
  ;i 
  form 
  included 
  under 
  the 
  Chaetopteridae 
  by 
  fli. 
  Claparede, 
  

   has 
  a 
  large 
  bilobed 
  flattened 
  snout 
  (Supplement, 
  ' 
  Les 
  Auuel. 
  Ch6topod< 
  

   du 
  Golfe 
  de 
  Naples,' 
  p. 
  120, 
  pi. 
  xi. 
  fig. 
  1). 
  

  

  