﻿408 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM. 
  vol. 
  44. 
  

  

  wide, 
  thin-walled 
  portion, 
  a 
  twisted 
  part 
  showing 
  a 
  tendency 
  to 
  form 
  

   a 
  coil, 
  and 
  a 
  straight 
  rectum, 
  on 
  which 
  a 
  small 
  diverticulum 
  is 
  found. 
  

   The 
  anus 
  lies 
  at 
  a 
  considerable 
  distance 
  (2 
  or 
  3 
  mm.) 
  in 
  front 
  of 
  the 
  

   nephrostome, 
  A 
  simple 
  Polian 
  tube 
  of 
  wide 
  caliber 
  extends 
  along 
  

   the 
  dorsal 
  side 
  of 
  the 
  esophagus 
  to 
  a 
  point 
  considerably 
  beyond 
  that 
  

   at 
  which 
  the 
  alimentary 
  tube 
  leaves 
  the 
  ventral 
  retractor. 
  

  

  The 
  single 
  (right) 
  nephridium 
  is 
  large, 
  and 
  extends 
  in 
  specimens 
  of 
  

   the 
  common 
  variety 
  about 
  half 
  the 
  distance 
  between 
  the 
  neplirostome 
  

   and 
  the 
  posterior 
  extremity 
  of 
  the 
  body. 
  It 
  is 
  closely 
  attached 
  along 
  

   its 
  ventral 
  line 
  to 
  the 
  wall 
  of 
  the 
  body 
  by 
  several 
  strands. 
  

  

  The 
  reproductive 
  organ 
  is 
  situated 
  on 
  the 
  right 
  side 
  of 
  the 
  post- 
  

   erior 
  end 
  of 
  the 
  body 
  cavity, 
  a 
  convoluted 
  ridge, 
  beginning 
  close 
  to 
  

   the 
  posterior 
  end 
  of 
  the 
  ventral 
  nerve 
  cord 
  and 
  extending 
  obliquely 
  

   over 
  the 
  base 
  of 
  the 
  right 
  root 
  of 
  the 
  ventral 
  retractor, 
  on 
  a 
  line 
  

   continuous 
  with 
  that 
  of 
  the 
  attachment 
  of 
  the 
  dorsal 
  retractor. 
  

  

  VARIETIES. 
  

  

  The 
  most 
  interesting 
  fact 
  in 
  regard 
  to 
  this 
  species 
  is 
  its 
  extraor- 
  

   dinary 
  plasticity, 
  its 
  tendency 
  to 
  form 
  modifications 
  and 
  probably 
  

   germinal 
  variations. 
  How 
  far 
  this 
  diversity 
  in 
  external 
  features 
  is 
  

   due 
  to 
  the 
  direct 
  action 
  of 
  the 
  environment, 
  as, 
  for 
  instance, 
  the 
  kinds 
  

   of 
  empty 
  shells 
  or 
  tubes 
  which 
  the 
  worms 
  inhabit, 
  their 
  food 
  supply, 
  

   temperature 
  of 
  the 
  water, 
  etc., 
  and 
  how 
  far 
  it 
  may 
  be 
  determined 
  by 
  

   heredity 
  are 
  questions 
  which 
  can 
  be 
  answered 
  fully, 
  of 
  course, 
  only 
  by 
  

   breeding 
  and 
  rearing 
  the 
  animals. 
  

  

  PHASCOLION 
  STROMBI 
  var. 
  TUBICOLA 
  (Verrill). 
  

  

  This 
  variety 
  is 
  identical 
  with 
  Phascolosoma 
  tuhicola 
  described 
  by 
  

   VerriQ 
  (1873) 
  as 
  a 
  new 
  species 
  based 
  on 
  certain 
  superficial 
  features 
  

   which 
  were 
  believed 
  to 
  distinguish 
  it 
  from 
  the 
  earlier 
  described 
  Pli. 
  

   csementarium 
  (Quatrefages). 
  I 
  have 
  dissected 
  a 
  sufficient 
  number 
  of 
  

   specimens 
  in 
  the 
  National 
  Museum 
  named 
  by 
  Verrill 
  "iuhicola" 
  to 
  

   determine 
  from 
  a 
  study 
  of 
  their 
  internal 
  as 
  well 
  as 
  external 
  structure 
  

   that 
  this 
  form 
  is 
  identical 
  with 
  Ph. 
  strombi, 
  of 
  which 
  it 
  is 
  a 
  local 
  

   variety 
  extending 
  from 
  Casco 
  Bay 
  to 
  the 
  waters 
  about 
  Cape 
  Ann. 
  

   I 
  have 
  retained 
  Verrill's 
  term 
  tuhicola 
  as 
  a 
  varietal 
  name 
  out 
  of 
  

   respect 
  for 
  the 
  rule 
  of 
  priority 
  in 
  nomenclature, 
  though 
  it 
  is 
  not 
  a 
  

   distinctive 
  descriptive 
  expression. 
  The 
  variety 
  that 
  I 
  have 
  called 
  

   "fusca," 
  for 
  example, 
  is 
  a 
  tubicolous 
  form 
  the 
  range 
  of 
  which 
  over- 
  

   laps 
  that 
  of 
  tuhicola. 
  A 
  better 
  descriptive 
  term 
  for 
  this 
  variety 
  would 
  

   be 
  pullacea. 
  

  

  Verrill 
  describes 
  it 
  as 
  having 
  the 
  posterior 
  end 
  of 
  the 
  body 
  " 
  trans- 
  

   versely 
  wrinkled 
  and 
  rough, 
  and 
  covered 
  with 
  small 
  round, 
  somewhat 
  

   raised 
  verrucas 
  or 
  suckers." 
  The 
  holdfasts, 
  or 
  triangular 
  chitinous 
  

   hooks, 
  are 
  said 
  to 
  be 
  more 
  numerous, 
  sharper, 
  and 
  darker-colored 
  

  

  