﻿138 
  E. 
  J. 
  ALLEN. 
  

  

  with 
  a 
  mass 
  of 
  spei'ra-cells 
  in 
  various 
  stages 
  of 
  development 
  

   and 
  of 
  spermatozoa. 
  

  

  The 
  spermatozoa 
  (fig. 
  53) 
  have 
  pear-shaped 
  heads, 
  rounded 
  

   in 
  front, 
  and 
  with 
  straight 
  posterior 
  ends, 
  to 
  which 
  the 
  

   flagella 
  are 
  attached. 
  A 
  deeply 
  staining 
  portion 
  at 
  the 
  

   posterior 
  end 
  of 
  the 
  head 
  (mi^.) 
  probably 
  represents 
  the 
  

   " 
  middle-piece. 
  '^ 
  

  

  The 
  Divisions 
  of 
  the 
  Body. 
  

  

  Now 
  that 
  a 
  description 
  has 
  been 
  given 
  both 
  of 
  the 
  external 
  

   characters 
  and 
  of 
  the 
  internal 
  anatomy 
  of 
  Poecilocha3tus, 
  

   we 
  are 
  in 
  a 
  position 
  to 
  discuss 
  more 
  fully 
  the 
  question 
  of 
  the 
  

   regions 
  into 
  which 
  the 
  body 
  of 
  the 
  worm 
  can 
  pi-operly 
  be 
  

   divided. 
  These 
  are 
  (1) 
  the 
  prostomium, 
  or 
  head; 
  (2) 
  an 
  

   anterior 
  region, 
  from 
  the 
  first 
  segment 
  to 
  the 
  eleventh 
  ; 
  (o) 
  

   an 
  intermediate 
  region, 
  comprising 
  segments 
  12, 
  13, 
  14, 
  15 
  

   and 
  16; 
  (4) 
  a 
  genital 
  region 
  commencing 
  at 
  segment 
  17 
  and 
  

   continuing 
  backwards 
  until 
  it 
  passes 
  gradually 
  into 
  (5) 
  the 
  

   terminal 
  region, 
  or 
  tail 
  segments, 
  and 
  (6) 
  the 
  pygidium. 
  

  

  1. 
  The 
  prostomiuni, 
  or 
  head, 
  has 
  alread}^ 
  been 
  de- 
  

   scribed. 
  To 
  it 
  must 
  be 
  reckoned 
  the 
  median 
  tentacle, 
  the 
  

   palps, 
  the 
  nuchal 
  organ 
  and 
  two 
  pairs 
  of 
  eyes. 
  

  

  2. 
  The 
  anterior 
  region 
  (segments 
  1 
  to 
  11) 
  is 
  character- 
  

   ised 
  by 
  the 
  straight, 
  muscular, 
  cylindrical 
  dorsal 
  vessel 
  ; 
  by 
  

   the 
  straight 
  and 
  muscular 
  oesophagus 
  and 
  pharynx; 
  by 
  the 
  

   presence, 
  excepting 
  in 
  segments 
  1 
  and 
  2, 
  of 
  nephridia 
  with 
  

   nephridiostomes, 
  but 
  without 
  genital 
  funnels 
  ; 
  by 
  the 
  absence 
  

   of 
  gonads; 
  by 
  the 
  backward 
  extension 
  of 
  the 
  septa 
  separating 
  

   the 
  body 
  segments 
  (segments 
  7 
  to 
  11), 
  and 
  consequent 
  great 
  

   elongation 
  of 
  the 
  lateral 
  blood-vessels 
  which 
  run 
  in 
  these 
  

   septa; 
  by 
  the 
  great 
  development 
  of 
  the 
  blind, 
  fingei'-shaped 
  

   vessels 
  given 
  off 
  from 
  each 
  lateral 
  vessel 
  into 
  the 
  segment 
  

   behind; 
  by 
  the 
  peculiar 
  modification 
  of 
  the 
  parapodial 
  cirri 
  

   (segments 
  7 
  to 
  11); 
  by 
  the 
  absence 
  of 
  hairy 
  bristles; 
  and 
  by 
  

   the 
  pear-shaped 
  lateral 
  sense-organs 
  protruding 
  from 
  the 
  

   surface 
  of 
  the 
  body. 
  

  

  