﻿616 
  rnocEEJUNfis 
  of 
  the 
  xatioxal 
  museum. 
  

  

  My 
  own 
  conclusions 
  in 
  regard 
  to 
  the 
  whole 
  matter 
  are 
  as 
  follows 
  : 
  

  

  1. 
  There 
  are 
  in 
  the 
  Philippines 
  a 
  number 
  of 
  closely 
  allied 
  species 
  of 
  

   biids, 
  each 
  of 
  wliich 
  lias 
  a 
  definite 
  range 
  that 
  in 
  many 
  instances 
  at 
  

   least 
  does 
  not 
  overlap 
  the 
  range 
  of 
  any 
  other 
  species 
  of 
  the 
  same 
  genus. 
  

   The 
  general 
  correspondence 
  between 
  the 
  ranges 
  of 
  these 
  species 
  and 
  

   the 
  i)ositioMS 
  of 
  geographical 
  barriers 
  to 
  their 
  free 
  migration 
  lends 
  

   probability 
  to 
  the 
  conclusion 
  that 
  we 
  are 
  here 
  dealing 
  with 
  a 
  case 
  of 
  

   cause 
  and 
  effect, 
  especially 
  when 
  we 
  remember 
  the 
  fact 
  that 
  the 
  i)he- 
  

   nomenon 
  is 
  not 
  an 
  isolated 
  one, 
  but 
  has 
  been 
  observed 
  in 
  the 
  Galapa- 
  

   gos 
  and 
  other 
  island 
  groui)s.' 
  

  

  2. 
  On 
  the 
  other 
  hand, 
  cases 
  where 
  two 
  or 
  more 
  closely 
  allied 
  si)ecies 
  

   of 
  the 
  same 
  genus 
  occur 
  within 
  the 
  limits 
  of 
  a 
  single 
  island 
  are 
  too 
  

   numerous 
  to 
  be 
  overlooked. 
  While 
  it 
  does 
  not 
  necessarily 
  follow 
  from 
  

   the 
  fact 
  that 
  two 
  species 
  occui)y 
  the 
  same 
  island 
  that 
  they 
  occupy 
  the 
  

   same 
  life 
  zone, 
  there 
  are 
  enough 
  well 
  ascertained 
  cases 
  where 
  two 
  allied 
  

   species 
  do 
  occuf 
  side 
  by 
  side 
  to 
  effectually 
  negative 
  Steere's 
  conclusion 
  

   that 
  the 
  genus 
  is 
  represented 
  by 
  but 
  a 
  single 
  species 
  in 
  a 
  place. 
  

  

  .'>. 
  We 
  are 
  more 
  likely 
  to 
  lind 
  genera 
  represented 
  hy 
  several 
  species 
  

   in 
  large 
  islands 
  with 
  diversified 
  surfaces 
  than 
  in 
  small 
  islands 
  in 
  which 
  

   comparatively 
  uniform 
  conditions 
  prevail, 
  and 
  in 
  islands 
  that 
  are 
  well 
  

   known 
  than 
  in 
  those 
  that 
  are 
  little 
  known. 
  

  

  4. 
  Among 
  the 
  facts 
  at 
  our 
  disposal 
  there 
  is 
  nothing 
  to 
  justify 
  the 
  

   statement 
  that 
  isolation 
  is 
  the 
  first 
  and 
  necessary 
  factor 
  in 
  species 
  

   formation, 
  since 
  we 
  have 
  no 
  proof 
  that 
  environment 
  is 
  the 
  direct 
  cause 
  

   of 
  variation, 
  -without 
  whicli 
  there 
  can 
  be 
  no 
  development. 
  

  

  5. 
  In 
  studying 
  island 
  avifaunae 
  it 
  should 
  be 
  remembered 
  that 
  geo- 
  

   graphical 
  barriers, 
  in 
  the 
  ordinary 
  sense, 
  are 
  not 
  the 
  only 
  barriers 
  

   which 
  are 
  effective 
  in 
  bringing 
  about 
  localization 
  of 
  birds. 
  Temi)era- 
  

   ture, 
  distribution 
  of 
  food 
  supply, 
  direction 
  of 
  prevailing 
  winds, 
  charac- 
  

   ter 
  and 
  duration 
  of 
  seasons, 
  and 
  especially 
  the 
  nature 
  and 
  distribution 
  

   of 
  enemies 
  are 
  of 
  importance 
  in 
  limiting 
  the 
  ranges 
  of 
  species, 
  and 
  

   must 
  be 
  taken 
  into 
  consideration 
  before 
  we 
  can 
  arrive 
  at 
  any 
  final 
  

   conclusions. 
  

  

  6. 
  If 
  two 
  closel}' 
  allied 
  species 
  were 
  thrown 
  together 
  in 
  an 
  island 
  one 
  

   of 
  three 
  things 
  would 
  happen. 
  They 
  would 
  continue 
  to 
  live 
  together, 
  

   preserving 
  their 
  relative 
  numbers, 
  or 
  they 
  would 
  fuse 
  with 
  each 
  other, 
  

   forming 
  a 
  hybrid 
  race, 
  or 
  one 
  species 
  would 
  tend 
  to 
  exterminate 
  the 
  

   other, 
  

  

  7. 
  I 
  do 
  not 
  at 
  present 
  know 
  of 
  any 
  positive 
  evidence 
  in 
  favor 
  of 
  

   Steere's 
  theory 
  that 
  they 
  would 
  fuse. 
  Similaritj^ 
  in 
  coloring, 
  or 
  in 
  the 
  

   food, 
  would 
  by 
  no 
  means 
  serve 
  to 
  offset 
  the 
  well-known 
  tendency 
  to 
  

   sterility 
  between 
  different 
  species, 
  and 
  especially 
  among 
  the 
  hybrid 
  

  

  'See 
  Wallafe's 
  ''Island 
  Life."' 
  Also 
  Moritz 
  Wauner, 
  Die 
  Darwiuiscbe 
  Theorie 
  

   imd 
  (las 
  Migrationgesetz 
  der 
  Oiganismen., 
  Leipzig, 
  1868: 
  Baur. 
  Eiii 
  Besxitb 
  dt-r 
  

   Galapagos-Iuselu. 
  Biol. 
  C«>utralbl., 
  XII, 
  p. 
  221, 
  1892; 
  Rid.owa\. 
  I'.irds 
  of 
  tlie 
  

   Galapagos 
  Arthiitelago., 
  Proc. 
  U. 
  S. 
  Nat. 
  Miis.. 
  XIX. 
  p. 
  4.^9. 
  1S97. 
  

  

  