﻿ADAPTIVENESS 
  AND 
  PURPOSIVENESS 
  323 
  

  

  i 
  

  

  sinking 
  in. 
  The 
  African 
  egg-eating 
  snake, 
  Dasypeltis, 
  has 
  

   very 
  few 
  teeth 
  and 
  it 
  would 
  not 
  be 
  profitable 
  to 
  crack 
  the 
  

   eggs 
  in 
  its 
  mouth; 
  the 
  egg 
  slips 
  intact 
  into 
  the 
  gullet, 
  where 
  

   it 
  is 
  met 
  by 
  the 
  sharp 
  points 
  of 
  the 
  inferior 
  spines 
  of 
  a 
  

   number 
  of 
  vertebrae. 
  These 
  project 
  into 
  the 
  gullet 
  and 
  cut 
  

   the 
  egg-shells, 
  so 
  that 
  none 
  of 
  the 
  precious 
  food 
  is 
  wasted. 
  

   The 
  spines 
  are 
  said 
  to 
  be 
  actually 
  tipped 
  with 
  enamel, 
  the 
  

   hardest 
  of 
  all 
  tissues. 
  The 
  empty 
  broken 
  egg-shells 
  are 
  

   always 
  returned. 
  

  

  An 
  adaptation 
  that 
  gives 
  us 
  pause 
  is 
  the 
  ' 
  egg-tooth 
  ' 
  

   found 
  at 
  the 
  tip 
  of 
  the 
  bill 
  in 
  many 
  young 
  birds, 
  and 
  used 
  

   by 
  them 
  to 
  break 
  a 
  way 
  through 
  the 
  imprisoning 
  egg-shell. 
  

   It 
  is 
  a 
  hard 
  thickening 
  of 
  horn 
  and 
  lime 
  at 
  the 
  tip 
  of 
  the 
  

   bill, 
  and 
  since 
  it 
  develops 
  before 
  the 
  horny 
  ensheathment 
  

   of 
  the 
  beak 
  it 
  may 
  be 
  a 
  residue 
  of 
  a 
  very 
  ancient 
  scaly 
  

   armature 
  in 
  Reptilian 
  ancestors 
  of 
  birds. 
  Be 
  this 
  as 
  it 
  

   may, 
  the 
  instrument 
  is 
  an 
  effective 
  one 
  and 
  it 
  is 
  used 
  only 
  

   once! 
  What 
  happens 
  is 
  this: 
  the 
  young 
  bird 
  ready 
  to 
  be 
  

   hatched 
  thrusts 
  its 
  beak 
  into 
  the 
  air-chamber 
  that 
  forms 
  

   at 
  the 
  broad 
  end 
  of 
  the 
  egg; 
  air 
  rushes 
  down 
  the 
  nostrils 
  

   and 
  fills 
  the 
  lungs 
  for 
  the 
  first 
  time; 
  in 
  the 
  exhilaration 
  

   of 
  this 
  first 
  breath 
  the 
  unhatched 
  bird 
  knocks 
  vigorously 
  

   at 
  the 
  shell 
  and 
  breaks 
  open 
  the 
  prison 
  doors. 
  After 
  a 
  few 
  

   days, 
  in 
  most 
  cases, 
  the 
  egg-tooth, 
  having 
  done 
  its 
  work, 
  falls 
  

   off, 
  a 
  well-adapted 
  instrument 
  that 
  functions 
  only 
  once. 
  

  

  But 
  there 
  is 
  a 
  further 
  detail 
  which 
  is 
  of 
  much 
  interest. 
  

   The 
  bill 
  and 
  its 
  egg-tooth 
  are 
  only 
  the 
  instruments; 
  what 
  

   about 
  the 
  musculature 
  which 
  works 
  these 
  ? 
  Prof. 
  Franz 
  

   Keibel 
  has 
  inquired 
  into 
  this 
  in 
  the 
  case 
  of 
  the 
  unhatched 
  

   chick 
  and 
  duckling. 
  He 
  finds 
  that 
  the 
  work 
  is 
  done 
  by 
  a 
  

   muscle 
  called 
  the 
  musculus 
  complexus, 
  and 
  that 
  this 
  is 
  very 
  

   markedly 
  hypertrophied 
  for 
  some 
  time 
  before 
  hatching. 
  On 
  

  

  