﻿THE 
  ANATOMY 
  OF 
  PCECILoOH-TlTU.S, 
  CLAPAKEnK. 
  139 
  

  

  It 
  will 
  be 
  noted 
  that 
  the 
  hiiuleniiost 
  segments 
  of 
  this 
  

   region 
  (7 
  to 
  11) 
  have 
  sevei-al 
  characters 
  which 
  distinguish 
  

   them 
  from 
  those 
  in 
  front. 
  These 
  are 
  the 
  backward 
  extension 
  

   of 
  the 
  septa, 
  the 
  presence 
  of 
  spiny 
  bristles, 
  which 
  are 
  absent 
  

   in 
  segments 
  1 
  to 
  6 
  (excepting 
  for 
  one 
  bristle 
  in 
  each 
  parapo- 
  

   dium 
  of 
  segment 
  2), 
  and 
  the 
  peculiar 
  modification 
  of 
  the 
  

   parapodial 
  cirri, 
  which 
  character 
  in 
  P. 
  fulgorisand 
  in 
  the 
  

   larvae 
  from 
  Norway 
  and 
  Normandy 
  is, 
  according 
  to 
  Claparede, 
  

   confined 
  exclusively 
  to 
  these 
  segments, 
  as 
  it 
  is 
  also 
  in 
  the 
  

   pelagic 
  larva3 
  of 
  Poeciloch 
  fetus 
  found 
  at 
  Plymouth. 
  

  

  3. 
  The 
  intermediate 
  region 
  (segments 
  12 
  to 
  16) 
  is 
  

   chiefly 
  noteworthy 
  from 
  the 
  presence 
  of 
  the 
  large, 
  contractile, 
  

   lateral 
  pouches 
  of 
  the 
  dorsal 
  vessel, 
  which 
  are 
  found 
  in 
  its 
  

   first 
  four 
  segments. 
  The 
  nepliridia 
  are 
  still 
  without 
  genital 
  

   funnels, 
  and 
  no 
  gonads 
  are 
  developed. 
  In 
  the 
  adult 
  P. 
  

   serpens 
  the 
  modified 
  parapodial 
  cirri 
  of 
  segments 
  7 
  to 
  11 
  

   extend 
  back 
  to 
  segments 
  12 
  and 
  13; 
  but 
  this 
  is 
  not 
  the 
  case 
  

   in 
  P. 
  fulgoris 
  nor 
  in 
  any 
  known 
  larvse 
  of 
  Poeciloch 
  ^tus. 
  

   In 
  the 
  latter 
  the 
  cirri 
  of 
  all 
  the 
  segments 
  in 
  this 
  region 
  have 
  

   the 
  conical 
  form 
  found 
  in 
  the 
  genital 
  region, 
  and 
  this 
  is 
  true 
  

   also 
  for 
  the 
  cirri 
  of 
  segments 
  14, 
  15 
  and 
  16 
  of 
  P. 
  serpens. 
  

  

  In 
  segments 
  12, 
  13, 
  14 
  and 
  15 
  the 
  segmental 
  enlargements 
  

   of 
  the 
  alimentary 
  canal 
  commence 
  to 
  appear, 
  becoming 
  more 
  

   pronounced 
  in 
  each 
  succeeding 
  segment, 
  whilst 
  in 
  segment 
  

   16 
  these 
  enlai-gements 
  are 
  fully 
  developed 
  and 
  the 
  intestine 
  

   is 
  completely 
  sui'rounded 
  by 
  a 
  blood-sinus, 
  the 
  dorsal 
  vessel 
  

   ceasing 
  to 
  exist. 
  

  

  The 
  hairy 
  bristles 
  of 
  the 
  genital 
  segments 
  are 
  absent 
  in 
  

   this 
  region 
  (12 
  — 
  16), 
  and 
  the 
  lateral 
  organs 
  still 
  protrude 
  

   from 
  the 
  body 
  surface 
  as 
  in 
  the 
  anterior 
  region. 
  

  

  4. 
  The 
  genital 
  region, 
  from 
  segment 
  17 
  to 
  within 
  about 
  

   thirty 
  segments 
  of 
  the 
  end 
  of 
  the 
  body 
  of 
  a 
  full-grown 
  worm, 
  

   is 
  characterised 
  by 
  the 
  presence 
  of 
  gonads 
  and 
  well-developed 
  

   genital 
  funnels; 
  by 
  the 
  large 
  intestinal 
  pouches 
  and 
  intestinal 
  

   blood-sinus 
  ; 
  by 
  the 
  presence 
  of 
  large 
  numbers 
  of 
  well- 
  

   developed 
  hairy 
  bristles 
  (figs. 
  14 
  and 
  16) 
  and 
  of 
  flattened, 
  

   membranous, 
  spined 
  bristles 
  (fig. 
  17), 
  which 
  commence 
  sud- 
  

  

  