﻿27 
  

  

  Mgk 
  r,a> 
  l-.voA- 
  

  

  Figure 
  8. 
  

   with 
  the 
  hinge 
  end 
  downwards 
  and 
  the 
  free 
  edges 
  of 
  the 
  

   valves 
  upwards 
  the 
  animals 
  are 
  in 
  an 
  excellent 
  position 
  

   to 
  feed 
  while 
  the 
  outside 
  vertical 
  surfaces 
  of 
  the 
  valves 
  

   are 
  well 
  adapted 
  to 
  aiford 
  x>laces 
  of 
  attachment 
  for 
  the 
  

   "spat." 
  The 
  latter 
  however 
  seems 
  to 
  attach 
  itself 
  in 
  the 
  

   greatest 
  abundance 
  to 
  the 
  old 
  oysters 
  fixed 
  at 
  the 
  sur- 
  

   face 
  of 
  the 
  bank. 
  If 
  one 
  removes 
  oysters 
  from 
  these 
  

   beds 
  tliey 
  are 
  found 
  to 
  adhere 
  together 
  in 
  clusters 
  as 
  

   shown 
  in 
  Figs, 
  4 
  and 
  ^ 
  

  

  Carefully 
  observing 
  the 
  char- 
  

  

  "-a 
  

  

  ---S 
  

  

  Figure 
  4. 
  Figure 
  5. 
  

  

  acters 
  presented 
  by 
  these 
  masses, 
  it 
  is 
  soon 
  noticed 
  that 
  

   they 
  consist 
  of 
  a 
  series 
  of 
  generations 
  which 
  have 
  grown 
  

   one 
  upon 
  the 
  other. 
  In 
  Fig. 
  4 
  four 
  generations 
  may 
  

   easily 
  be 
  made 
  out, 
  as 
  indicated 
  by 
  the 
  letters 
  a, 
  b, 
  c, 
  d: 
  

   in 
  ascending 
  order 
  the 
  oldest 
  generation 
  a, 
  is 
  represent- 
  

   ed 
  by 
  dead 
  shells, 
  which 
  are 
  buried 
  in 
  a 
  black, 
  sandy 
  

   material, 
  which 
  has 
  acquired 
  solidity 
  from 
  the 
  large 
  

   quantity 
  of 
  imbedded 
  dead 
  shells 
  which 
  it 
  contains. 
  

   Attached 
  to 
  the 
  upper 
  edges 
  of 
  the 
  dead 
  valves 
  of 
  a 
  fol- 
  

   lows 
  generation 
  h, 
  which 
  consists 
  in 
  part 
  of 
  living 
  and 
  

   in 
  part 
  of 
  the 
  shells 
  of 
  dead 
  animals 
  ; 
  on 
  the 
  preceding 
  

   the 
  living 
  uppermost 
  generation 
  c 
  is 
  fixed, 
  which 
  affords 
  

   attachment 
  to 
  a 
  generation 
  of 
  young 
  d, 
  though 
  where 
  

   there 
  are 
  open 
  cavities 
  the 
  lower 
  generations 
  may 
  bear 
  

  

  