﻿612 
  FBOCEEDINGS 
  OF 
  THE 
  NATIOXAL 
  MUSEUM. 
  

  

  The 
  islands 
  from 
  which 
  the 
  smallest 
  number 
  of 
  genera 
  is 
  known, 
  

   then, 
  afford 
  the 
  strongest 
  confirmation 
  of 
  Steere's 
  law. 
  

  

  As 
  we 
  pass 
  to 
  the 
  larger 
  and 
  better 
  known 
  islands, 
  the 
  broken 
  line 
  

   takes 
  permanent 
  leave 
  of 
  the 
  zero 
  level, 
  and 
  the 
  solid 
  line 
  of 
  the 
  100 
  per 
  

   cent 
  mark. 
  It 
  will 
  be 
  noted, 
  however, 
  that 
  on 
  the 
  average 
  the 
  solid 
  line 
  

   keeps 
  well 
  above 
  the 
  50 
  per 
  cent 
  mark. 
  The 
  first 
  thing 
  that 
  calls 
  for 
  

   sjiecial 
  attention 
  is 
  its 
  sudden 
  drop 
  to 
  27 
  jier 
  cent 
  for 
  Siquijor, 
  and 
  the 
  

   corresponding 
  rise 
  in 
  the 
  broken 
  line. 
  Reference 
  to 
  the 
  tables 
  will 
  show 
  

   that 
  this 
  result 
  is 
  due 
  not 
  so 
  much 
  to 
  a 
  larger 
  number 
  of 
  exceptions 
  to 
  

   Steere's 
  law 
  from 
  Table 
  B, 
  as 
  to 
  an 
  unusually 
  small 
  number 
  of 
  confirma- 
  

   tions 
  (oidy 
  three) 
  from 
  Table 
  A. 
  

  

  I 
  have 
  already 
  stated 
  my 
  reasons 
  for 
  believing 
  that 
  Siquijor 
  is 
  an 
  

   island 
  of 
  very 
  recent 
  origin, 
  and 
  has 
  not 
  been 
  connected 
  with 
  any 
  of 
  

   the 
  adjacent 
  islands 
  since 
  it 
  received 
  its 
  present 
  bird 
  fauna. 
  I 
  believe 
  

   it 
  can 
  be 
  shoAvn 
  that 
  the 
  birds 
  distributed 
  according 
  to 
  Steere's 
  law 
  are, 
  

   as 
  a 
  rule, 
  possessed 
  of 
  comparatively 
  weak 
  power 
  of 
  flight, 
  and 
  this 
  

   probably 
  accounts 
  for 
  their 
  not 
  having 
  reached 
  Siquijor 
  in 
  larger 
  num- 
  

   bers. 
  The 
  divergence 
  of 
  the 
  two 
  lines 
  for 
  Marinduque, 
  and 
  their 
  

   approximation 
  for 
  Bohol 
  find 
  their 
  explanation 
  in 
  the 
  facts 
  already 
  

   stated 
  in 
  regard 
  to 
  these 
  islands. 
  Again, 
  it 
  will 
  be 
  noted 
  that 
  the 
  

   curve 
  becomes 
  more 
  regular 
  as 
  we 
  pass 
  to 
  the 
  larger 
  and 
  better 
  known 
  

   islands, 
  the 
  broken 
  line 
  steadily 
  rising 
  as 
  the 
  solid 
  one 
  falls. 
  

  

  The 
  evidence 
  furnished 
  by 
  Curve 
  II, 
  then, 
  confirms 
  that 
  obtained 
  from 
  

   Curve 
  I. 
  On 
  the 
  strength 
  of 
  it 
  we 
  may 
  make 
  the 
  statement 
  that 
  the 
  

   larger 
  and 
  more 
  diversified 
  the 
  island, 
  the 
  larger 
  will 
  be 
  the 
  average 
  

   number 
  of 
  species 
  into 
  which 
  the 
  genera 
  of 
  Table 
  D 
  are 
  differentiated, 
  

   and 
  the 
  larger 
  will 
  be 
  the 
  percentage 
  of 
  genera 
  represented 
  by 
  two 
  or 
  

   more 
  species 
  as 
  compared 
  with 
  those 
  represented 
  by 
  but 
  a 
  single 
  

   species. 
  

  

  I 
  have 
  shown 
  that 
  a 
  majority 
  both 
  of 
  genera 
  and 
  species 
  are 
  dis- 
  

   tributed 
  in 
  opposition 
  to 
  Steere's 
  law. 
  How 
  then 
  are 
  we 
  to 
  explain 
  the 
  

   fact 
  that 
  the 
  solid 
  line 
  in 
  Curve 
  II, 
  indicating 
  the 
  percentage 
  of 
  genera 
  

   in 
  each 
  island 
  distributed 
  according 
  to 
  this 
  law, 
  is 
  well 
  above 
  the 
  50 
  

   per 
  cent 
  mark? 
  

  

  The 
  answer 
  to 
  this 
  question 
  is 
  found 
  in 
  part 
  in 
  the 
  fact 
  that 
  two 
  

   species 
  of 
  a 
  genus 
  may, 
  and 
  not 
  infrequently 
  do, 
  have 
  ranges 
  that 
  are 
  

   distinct 
  for 
  the 
  most 
  part, 
  but 
  overlap 
  along 
  their 
  line 
  of 
  contact, 
  so 
  

   that 
  the 
  sj^ecies 
  in 
  question 
  afford 
  exceptions 
  to 
  Steere's 
  law 
  in 
  only 
  a 
  

   part 
  of 
  the 
  islands 
  in 
  which 
  they 
  occur. 
  An 
  additional 
  and 
  very 
  

   important 
  reason 
  for 
  this 
  apparent 
  contradiction 
  will 
  readily 
  suggest 
  

   itself. 
  

  

  To 
  find 
  ten 
  exceptions 
  to 
  Steere's 
  law 
  we 
  must 
  collect 
  at 
  the 
  very 
  

   least 
  twenty 
  species 
  of 
  birds, 
  while 
  ten 
  species 
  may 
  suffice 
  to 
  afford 
  ten 
  

   confirmations 
  of 
  it. 
  If, 
  then, 
  genera 
  distributed 
  in 
  the 
  two 
  ways 
  were 
  

   equally 
  abundant 
  upon 
  an 
  island, 
  we 
  should 
  at 
  first 
  find 
  at 
  least 
  two 
  

   confirmations 
  of 
  Steere's 
  law 
  for 
  every 
  exception. 
  Keally, 
  however, 
  

  

  