﻿parasitic 
  on 
  on 
  Octojjus. 
  475 
  

  

  Pol'/jnis 
  ergasticus 
  from 
  tlie 
  west 
  coast 
  of 
  Ireland, 
  600- 
  

   700 
  fathoms. 
  

  

  Tlie 
  occurrence 
  of 
  a 
  parasitic 
  Harpacticid 
  in 
  the 
  unusual 
  

   situation 
  in 
  which 
  this 
  speries 
  was 
  found, 
  though 
  not 
  so 
  

   strange 
  as 
  is 
  the 
  case 
  of 
  JBahenophilus, 
  described 
  by 
  Auri- 
  

   villius 
  from 
  the 
  baleen 
  plates 
  of 
  the 
  blue 
  whale, 
  is 
  not 
  without 
  

   interest, 
  and 
  the 
  two 
  species 
  may 
  well 
  be 
  compared. 
  In 
  both 
  

   instances 
  we 
  have 
  isolated 
  species 
  belonging 
  to, 
  or 
  closely 
  

   allied 
  to, 
  non-parasitic 
  families, 
  specially 
  modi 
  tied 
  for 
  an 
  unusual 
  

   manner 
  of 
  life. 
  In 
  Cholidya 
  the 
  modification 
  has 
  gone 
  much 
  

   further 
  than 
  in 
  J3alcvnophtluf>', 
  and, 
  had 
  not 
  the 
  first 
  pair 
  of 
  

   feet 
  remained 
  unmodified, 
  the 
  relationship 
  to 
  Idt/a 
  might 
  

   liave 
  been 
  overlooked, 
  as 
  most 
  of 
  the 
  other 
  appendages, 
  taken 
  

   separately, 
  are 
  common 
  to 
  other 
  groups, 
  both 
  parasitic 
  and 
  

   free-living. 
  In 
  JBalcenophilus, 
  on 
  the 
  other 
  hand, 
  the 
  ad;i[)ta- 
  

   tions 
  to 
  its 
  peculiar 
  mode 
  of 
  life 
  are 
  so 
  slight 
  that 
  its 
  relation- 
  

   ship 
  to 
  Harpacticus 
  is 
  at 
  once 
  apparent, 
  and 
  it 
  would 
  be 
  

   difficult 
  to 
  m;dve 
  sure 
  that 
  it 
  had 
  a 
  jiarasilic 
  habit 
  were 
  its 
  

   place 
  of 
  origin 
  unknown. 
  The 
  genus 
  /r///^/, 
  by 
  the 
  possession 
  

   of 
  strongly 
  chelate 
  maxillse 
  and 
  maxillipedes, 
  seems 
  well 
  

   adapted 
  to 
  give 
  rise 
  to 
  a 
  parasitic 
  race, 
  as 
  the 
  means 
  of 
  

   attachment 
  are 
  already 
  present. 
  

  

  These 
  instances 
  of 
  paiasitic 
  forms 
  — 
  as 
  it 
  were, 
  in 
  the 
  

   niakino- 
  — 
  throw 
  some 
  light 
  on 
  the 
  oriuin 
  ot 
  tlie 
  various 
  families 
  

   of 
  parasitic 
  CJopepoda 
  in 
  general, 
  many 
  of 
  which, 
  it 
  is 
  probable, 
  

   have 
  started 
  independently 
  as 
  modifications 
  of 
  widely 
  separated 
  

   non-parasitic 
  species. 
  

  

  EXPLANATION 
  OF 
  PLATE 
  XXI. 
  

  

  