﻿No.ii:!4. 
  PHILIFPiyE 
  ORSlTHOLOGY—WOIiCESTEE 
  AND 
  BOUIiXS. 
  599 
  

  

  4. 
  The 
  line 
  between 
  the 
  Pliilippiue 
  and 
  Formosau 
  islands 
  also 
  remains 
  

   to 
  be 
  determined. 
  

  

  5. 
  The 
  Philippiues 
  can 
  not 
  be 
  divided 
  into 
  a 
  nnmber 
  of 
  zoologically 
  

   equivalent 
  groups, 
  but 
  do 
  naturally 
  fall 
  into 
  groups, 
  some 
  of 
  which 
  are 
  

   much 
  less 
  sharply 
  differentiated 
  than 
  others. 
  

  

  A 
  close 
  relationship 
  exists 
  between 
  the 
  degree 
  of 
  difference 
  in 
  the 
  

   avifauuae 
  of 
  any 
  two 
  groups 
  and 
  their 
  present 
  and 
  i)ast 
  geographical 
  

   relationship, 
  those 
  islands 
  which 
  have 
  been 
  longest 
  and 
  most 
  completely 
  

   cut 
  off 
  from 
  their 
  neighbors 
  showing 
  the 
  highest 
  degree 
  of 
  differentia- 
  

   tion. 
  In 
  this 
  connection 
  it 
  is 
  needless 
  to 
  remark 
  that 
  the 
  depth 
  of 
  

   channels 
  is 
  much 
  more 
  important 
  than 
  their 
  width 
  in 
  estimating 
  the 
  

   probable 
  duration 
  of 
  isolation. 
  

  

  C. 
  The 
  Central 
  Philippines, 
  comprising 
  the 
  islands 
  Negros, 
  Panay, 
  

   Guimaras, 
  and 
  Masbate, 
  form 
  a 
  well-detined 
  natural 
  group, 
  though 
  in 
  

   the 
  case 
  of 
  Masbate 
  there 
  are 
  indications 
  of 
  immigration 
  from 
  Luzon. 
  

  

  7. 
  Cebu 
  can 
  not 
  be 
  regarded 
  as 
  one 
  of 
  the 
  central 
  group. 
  It 
  is 
  sepa- 
  

   rated 
  from 
  i*^egros 
  by 
  a 
  very 
  deep 
  though 
  narrow 
  channel, 
  and 
  must 
  be 
  

   given 
  a 
  place 
  by 
  itself. 
  It 
  shows 
  a 
  slight 
  admixture 
  of 
  eastern 
  and 
  

   southern 
  forms. 
  

  

  8. 
  Siquijor 
  is 
  an 
  island 
  of 
  very 
  recent 
  origin. 
  It 
  has 
  been 
  populated 
  

   by 
  stragglers 
  from 
  other 
  islands, 
  and 
  its 
  three 
  peculiar 
  species 
  have 
  

   been 
  developed 
  from 
  allied 
  forms 
  under 
  the 
  iuduence 
  of 
  changed 
  

   environment. 
  

  

  9. 
  Tablas, 
  Romblon, 
  and 
  ^^ibuyan 
  show 
  no 
  evidence 
  of 
  having 
  been 
  

   connected 
  with 
  any 
  of 
  the 
  larger 
  islands. 
  Tablas 
  and 
  Romblon 
  should 
  

   probably 
  be 
  classed 
  together. 
  

  

  10. 
  There 
  are 
  abundant 
  evidences 
  of 
  the 
  original 
  distinctness 
  of 
  the 
  

   faunae 
  of 
  Luzon 
  and 
  Mindoro, 
  which 
  may 
  be 
  expected 
  to 
  increase 
  as 
  

   our 
  knowledge 
  of 
  Mindoro 
  birds 
  increases. 
  

  

  11. 
  Bougao, 
  Tawi 
  Tawi, 
  Lapac, 
  Siassi, 
  and 
  Sulu 
  form 
  another 
  natural 
  

   group, 
  to 
  which 
  Sibutu 
  must 
  probably 
  be 
  added. 
  The 
  diflfereuces 
  

   between 
  the 
  birds 
  of 
  this 
  group 
  and 
  those 
  of 
  Mindanao 
  and 
  Basilan 
  

   are 
  great. 
  

  

  12. 
  Stretching 
  from 
  Basilan 
  to 
  Luzon 
  we 
  have 
  a 
  chain 
  of 
  islands 
  

   between 
  which 
  the 
  zoological 
  relationship 
  is 
  very 
  close. 
  This 
  is 
  proven 
  

   by 
  the 
  mammals 
  as 
  well 
  as 
  by 
  the 
  birds, 
  such 
  genera 
  as 
  Seiurus, 
  Gal- 
  

   eopUhecus^ 
  and 
  Tarsius 
  extending 
  throughout 
  the 
  chain, 
  although 
  not 
  

   found 
  in 
  the 
  central 
  and 
  western 
  islands. 
  

  

  13. 
  Basilan 
  probably 
  at 
  one 
  time 
  formed 
  a 
  part 
  of 
  Mindanao. 
  It 
  has 
  

   been 
  separated 
  long 
  enough 
  to 
  allow 
  of 
  the 
  development 
  of 
  a 
  number 
  

   of 
  representative 
  forms 
  from 
  Mindanao 
  species. 
  A 
  considerable 
  num- 
  

   ber 
  of 
  species 
  have 
  a[)[)arently 
  entered 
  Mindanao 
  since 
  Basilan 
  was 
  cut 
  

   off', 
  and 
  have 
  hence 
  failed 
  to 
  gain 
  a 
  foothold 
  in 
  the 
  latter 
  island. 
  

  

  11. 
  The 
  relationship 
  between 
  the 
  birds 
  of 
  Mindanao 
  and 
  those 
  of 
  

   Samar 
  and 
  Ley 
  te 
  is 
  very 
  close, 
  though 
  possibly 
  less 
  so 
  than 
  that 
  between 
  

   those 
  of 
  Mindanao 
  and 
  Basilan. 
  

  

  