﻿Variation 
  in 
  Shape 
  of 
  the 
  Eggs 
  of 
  Birds. 
  359 
  

  

  XXXII. 
  — 
  On 
  the 
  Cause 
  of 
  Variation 
  in 
  the 
  Shape 
  of 
  the 
  

   Eggs 
  of 
  Birds. 
  By 
  Henry 
  Seebohm. 
  

  

  An 
  article 
  on 
  the 
  shape 
  of 
  the 
  eggs 
  of 
  birds 
  by 
  Dr. 
  Nicolsky, 
  

   Professor 
  of 
  Zoology 
  in 
  the 
  University 
  of 
  St. 
  Petersburg, 
  has 
  

   recently 
  been 
  published 
  in 
  the 
  ' 
  Revue 
  des 
  Sciences 
  natu- 
  

   relles 
  ' 
  of 
  that 
  city 
  *. 
  

  

  Roughly 
  speaking, 
  it 
  may 
  be 
  said 
  that 
  birds^ 
  eggs 
  in 
  shape 
  

   are 
  of 
  one 
  of 
  three 
  forms 
  : 
  — 
  

  

  1st. 
  Round 
  or 
  apple-shaped, 
  such 
  as 
  those 
  of 
  Falcons, 
  

   Owls, 
  and 
  Kingfishers. 
  

  

  2nd. 
  Oval 
  or 
  plum-shaped, 
  as 
  are 
  those 
  of 
  Pigeons, 
  Night- 
  

   jars, 
  Cormorants, 
  and 
  others. 
  

  

  3rd. 
  Pyriform 
  or 
  pear-shaped, 
  as 
  those 
  of 
  Waders. 
  

  

  Dr. 
  Nicolsky 
  has 
  invented 
  a 
  formula 
  by 
  which 
  the 
  shape 
  

   of 
  each 
  egg 
  may 
  be 
  broadly 
  expressed. 
  This 
  formula 
  consists 
  

   of 
  a 
  fraction, 
  the 
  numerator 
  of 
  which 
  represents 
  the 
  greatest 
  

   breadth 
  of 
  the 
  egg, 
  assuming 
  1000 
  to 
  be 
  the 
  greatest 
  

   length, 
  and 
  the 
  denominator 
  of 
  which 
  is 
  the 
  distance 
  of 
  the 
  

   centre 
  of 
  the 
  egg 
  at 
  its 
  greatest 
  breadth 
  from 
  the 
  obtuse 
  end, 
  

   on 
  the 
  same 
  assumption. 
  The 
  formula 
  of 
  a 
  perfectly 
  

   spherical 
  egg, 
  according 
  to 
  this 
  plan, 
  would 
  be 
  \^\f;*^)^ 
  ; 
  that 
  of 
  

   an 
  oval 
  egg, 
  in 
  "which 
  the 
  breadth 
  was 
  only 
  half 
  its 
  length, 
  

   would 
  be 
  ^00 
  J 
  whilst 
  that 
  of 
  a 
  very 
  pear-shaped 
  egg 
  might 
  

  

  "*= 
  3 
  33* 
  

  

  Dr. 
  Nicolsky 
  has 
  also 
  invented 
  a 
  hypothesis 
  to 
  account 
  for 
  

   the 
  variation 
  in 
  the 
  shape 
  of 
  birds' 
  eggs. 
  He 
  suggests 
  that 
  

   the 
  normal 
  shape 
  of 
  the 
  egg 
  is 
  spherical, 
  and 
  that 
  it 
  becomes 
  

   elongated 
  by 
  the 
  pressure 
  on 
  it 
  of 
  the 
  wall 
  of 
  the 
  ovary 
  

   before 
  the 
  calcai'cous 
  shell 
  is 
  deposited. 
  

  

  He 
  suggests 
  that 
  birds 
  which 
  lay 
  round 
  eggs 
  usually 
  keep 
  

   to 
  a 
  vertical 
  position, 
  in 
  which 
  the 
  weight 
  of 
  the 
  egg 
  counter- 
  

   acts 
  the 
  pressure 
  of 
  the 
  ovary, 
  and 
  that 
  those 
  which 
  lay 
  oval 
  

   eggs 
  usually 
  maintain 
  a 
  horizontal 
  position, 
  during 
  Avhich 
  

   the 
  weight 
  of 
  the 
  egg 
  assists 
  the 
  pressure 
  of 
  the 
  ovary. 
  He 
  

   further 
  suggests 
  that 
  pyriform 
  eggs 
  are 
  laid 
  by 
  birds 
  which 
  

   frequently 
  change 
  their 
  position, 
  like 
  the 
  Guillemot, 
  which 
  

   * 
  Si>e 
  'Cosmos, 
  Eovue 
  des 
  Sciences,' 
  no. 
  411, 
  p. 
  32 
  (Dec. 
  10, 
  1801) 
  ; 
  

   also 
  ' 
  Nature,' 
  vol. 
  xlvii. 
  y. 
  253 
  (1893). 
  

  

  