﻿IV. 
  CONDITIONS 
  GOVERNING 
  EXISTENCE 
  AND 
  GROWTH 
  OF 
  THE 
  

   SOFT 
  CLAM 
  (MYA 
  ARENARIA). 
  

  

  By 
  James 
  L. 
  Kellogg, 
  

   Professor' 
  of 
  Zoology, 
  Williams 
  College. 
  

  

  An 
  examination 
  of 
  any 
  extensive 
  clam-flat 
  will 
  reveal 
  the 
  presence 
  

   of 
  clams 
  only 
  in 
  certain 
  localities. 
  This 
  would 
  be 
  true 
  where 
  digging- 
  

   bad 
  not 
  been 
  excessive, 
  or 
  even 
  where 
  there 
  had 
  been 
  no 
  digging. 
  It 
  

   perhaps 
  would 
  be 
  impossible 
  to-day 
  to 
  find 
  large 
  flats 
  which 
  are 
  not 
  

   dug, 
  but 
  if 
  it 
  were 
  possible, 
  clams 
  would 
  be 
  found 
  only 
  here 
  and 
  there, 
  

   large 
  parts 
  of 
  the 
  flats 
  being 
  barren. 
  Certain 
  areas, 
  too, 
  bear 
  clams 
  

   for 
  a 
  number 
  of 
  years, 
  and 
  then 
  become 
  barren, 
  even 
  when 
  not 
  dug 
  

   excessively, 
  and 
  this 
  might 
  happen 
  if 
  the}^ 
  were 
  never 
  molested. 
  We 
  

   may 
  sometimes 
  witness, 
  also, 
  the 
  gradual 
  appearance 
  and 
  establish- 
  

   ment 
  of 
  clams 
  on 
  patches 
  of 
  bottom 
  which 
  had 
  previously 
  been 
  unpro- 
  

   ductive 
  for 
  long 
  periods. 
  

  

  Without 
  taking 
  into 
  account 
  the 
  all-powerful 
  human 
  factor, 
  we 
  may 
  

   believe 
  with 
  certainty 
  that 
  the 
  clam 
  perpetuates 
  itself 
  only 
  by 
  over- 
  

   coming 
  many 
  adverse 
  circumstances, 
  or 
  more 
  properly, 
  by 
  being 
  able 
  

   to 
  take 
  advantage 
  of 
  favorable 
  conditions 
  when 
  they 
  happen 
  to 
  arise. 
  

   It 
  of 
  course 
  is 
  true 
  of 
  all 
  organisms 
  that 
  they 
  require, 
  for 
  existence, 
  

   certain 
  very 
  definite 
  and 
  often 
  complicated 
  conditions 
  in 
  their 
  sur 
  

   roundings, 
  and 
  that 
  they 
  will 
  not 
  be 
  found 
  where 
  the 
  peculiar 
  combi- 
  

   nation 
  of 
  required 
  circumstances 
  and 
  conditions 
  is 
  not 
  present. 
  We 
  

   search 
  for 
  a 
  certain 
  species 
  of 
  violet 
  not 
  on 
  open 
  unshaded 
  marshes, 
  

   nor 
  in 
  high 
  sandy 
  woods, 
  but 
  in 
  the 
  rich 
  earth 
  of 
  woods 
  which 
  contains 
  

   a 
  large 
  amount 
  of 
  moisture 
  in 
  the 
  spring 
  when 
  the 
  plant 
  is 
  in 
  blossom. 
  

  

  In 
  looking 
  out 
  over 
  a 
  great 
  expanse 
  of 
  sand 
  which 
  is 
  exposed 
  at 
  low 
  

   tide 
  one 
  is 
  impressed 
  with 
  its 
  monotony. 
  There 
  is 
  here 
  no 
  contrast 
  

   of 
  light 
  and 
  shade. 
  There 
  are 
  no 
  elevations, 
  and 
  nothing 
  to 
  suggest 
  

   ravines 
  or 
  valleys 
  except 
  the 
  narrow 
  gutters 
  which 
  carry 
  off 
  the 
  last 
  

   of 
  the 
  retreating 
  tide. 
  It 
  requires 
  a 
  closer 
  scrutiny 
  to 
  reveal 
  any 
  

   vegetation 
  whatever, 
  though 
  it 
  is 
  present 
  in 
  places, 
  and 
  plays, 
  as 
  will 
  

   be 
  shown, 
  an 
  important 
  part 
  in 
  determining 
  the 
  existence 
  of 
  the 
  clam. 
  

   Everything 
  seems 
  to 
  be 
  equally 
  and 
  monotonously 
  exposed, 
  and 
  flat 
  

   and 
  barren. 
  Yet 
  the 
  conditions 
  are 
  not 
  b}^ 
  any 
  means 
  the 
  same 
  in 
  all 
  

   parts 
  of 
  the 
  flat. 
  The 
  variations 
  in 
  character 
  of 
  bottom 
  and 
  tide 
  are 
  

   so 
  great 
  that 
  clams 
  may 
  exist 
  in 
  one 
  spot, 
  the 
  boundaries 
  of 
  which 
  are 
  

   sharply 
  drawn, 
  and 
  may 
  not 
  live 
  in 
  others. 
  

  

  195 
  

  

  