﻿28 
  

  

  spat 
  as 
  indicated 
  at 
  e. 
  Whether 
  it 
  is 
  proper 
  to 
  regard 
  

   the 
  superimposed 
  series 
  of 
  individuals 
  as 
  generations 
  

   may 
  be 
  questioned, 
  but 
  as 
  no 
  more 
  expressive 
  word 
  

   occurs 
  to 
  me, 
  I 
  wish 
  to 
  be 
  understood 
  as 
  using 
  it 
  here 
  

   with 
  qualifications. 
  

  

  The 
  ""spat,"' 
  upon 
  careful 
  examination 
  of 
  these 
  beds, 
  

   w^e 
  learn 
  does 
  not 
  fix 
  itself 
  in 
  any 
  constant 
  position 
  ; 
  in 
  

   some 
  cases 
  the 
  young 
  may 
  have 
  the 
  hinge 
  of 
  the 
  shell 
  

   directed 
  downwards, 
  upwards, 
  or 
  to 
  the 
  right 
  or 
  left 
  

   hand. 
  Curiously 
  enough 
  the 
  shells 
  do 
  not 
  grow 
  in 
  the 
  

   directions 
  in 
  which 
  the 
  free 
  edges 
  of 
  the 
  valves 
  are 
  made 
  

   to 
  assume 
  in 
  the 
  young. 
  Should 
  the 
  young 
  happen 
  to 
  

   be 
  fixed 
  hinge 
  downwards 
  the 
  free 
  edges 
  of 
  the 
  valves 
  

   grow 
  directly 
  upwards 
  ; 
  in 
  case 
  the 
  hinge 
  is 
  directed 
  

   either 
  to 
  the 
  right 
  or 
  to 
  the 
  left 
  the 
  layers 
  of 
  lime 
  will 
  

   be 
  deposited 
  in 
  such 
  a 
  way 
  upon 
  one 
  side 
  as 
  to 
  cause 
  the 
  

   free 
  edges 
  of 
  the 
  valves 
  to 
  be 
  eventually 
  directed 
  up- 
  

   wards, 
  causing 
  the 
  umbonal 
  portion 
  of 
  the 
  valves 
  to 
  

   describe 
  an 
  arc 
  of 
  9()*-\ 
  In 
  case 
  the 
  hinge 
  is 
  at 
  first 
  

   directed 
  upwards 
  the 
  layers 
  of 
  carbonate 
  of 
  lime 
  will 
  be 
  

   deposited 
  in 
  such 
  a 
  way 
  by 
  the 
  mantle 
  as 
  to 
  bring 
  the 
  

   mouth 
  of 
  the 
  shell 
  upwards 
  as 
  shown 
  in 
  the 
  individual 
  a 
  

   Fig. 
  5. 
  The 
  attempt 
  to 
  get 
  into 
  a 
  vertical 
  position 
  has 
  

   only 
  been 
  partially 
  successful 
  however, 
  in 
  this 
  last 
  case, 
  

   since 
  the 
  arc 
  of 
  18(F 
  seems 
  a 
  little 
  too 
  much 
  to 
  be 
  tra- 
  

   versed 
  in 
  this 
  way, 
  even 
  by 
  the 
  wonderful 
  persistence 
  of 
  

   effort 
  of 
  the 
  inhabitant. 
  This 
  struggle 
  to 
  assume 
  the 
  

   upright 
  position 
  is 
  shown 
  by 
  the 
  curved 
  umbos 
  and 
  lines 
  

   of 
  growth 
  in 
  other 
  individuals, 
  both 
  old 
  and 
  young, 
  as 
  

   indicated 
  in 
  the 
  cases 
  of 
  b 
  c. 
  Pig 
  5. 
  The 
  habit 
  of 
  grow- 
  

   ing 
  in 
  the 
  erect 
  position, 
  where 
  the 
  banks 
  are 
  prolific 
  

   and 
  undisturbed 
  causes 
  the 
  individuals 
  to 
  be 
  very 
  much 
  

   crowded 
  together, 
  so 
  that 
  they 
  do 
  not 
  have 
  a 
  chance 
  to 
  

   expand 
  laterally. 
  From 
  this 
  cause 
  the 
  individual 
  oys- 
  

   ters 
  become 
  very 
  narrow 
  and 
  greatly 
  elongated 
  ; 
  the 
  

   peculiar 
  forms 
  which 
  result 
  are 
  known 
  as 
  "cat's- 
  

   tongues" 
  amongst 
  oystermen, 
  probably 
  from 
  a 
  sugges- 
  

  

  