﻿418 
  EEPOET 
  OF 
  COMMISSIONEE 
  OF 
  FISH 
  AND 
  FISHEEIES. 
  [38] 
  

  

  mal 
  position 
  with 
  the 
  umbo 
  directed 
  to 
  the 
  left. 
  This 
  figure 
  may 
  be 
  

   advantageously 
  compared, 
  in 
  respect 
  to 
  the 
  points 
  raised 
  here, 
  with 
  the 
  

   figure 
  of 
  the 
  external 
  anatomy 
  of 
  the 
  adult 
  on 
  Plate 
  LXXIII 
  in 
  my 
  

   " 
  Sketch 
  of 
  the 
  life-history 
  of 
  the 
  oyster," 
  already 
  cited. 
  Such 
  a 
  com- 
  

   parison 
  will 
  at 
  once 
  demonstrate 
  that 
  the 
  curvature 
  of 
  the 
  umbones 
  of 
  

   both 
  the 
  larval 
  shell 
  and 
  of 
  the 
  adult 
  is 
  toward 
  the 
  left. 
  This 
  I 
  find 
  to 
  

   be 
  uniformly 
  the 
  case 
  with 
  the 
  adults, 
  and 
  in 
  the 
  specimen 
  which 
  had 
  

   affixed 
  itself 
  to 
  the 
  brick 
  for 
  the 
  second 
  time 
  I 
  also 
  find 
  that 
  the 
  rule 
  

   holds. 
  

  

  Mr. 
  Cunningham's 
  inference 
  that 
  the 
  left 
  valve, 
  usually 
  regarded 
  as 
  

   the 
  lower 
  one, 
  is 
  really 
  the 
  upper, 
  because 
  he 
  finds 
  worm-tubes 
  and 
  hy- 
  

   droids 
  most 
  abundant 
  on 
  the 
  convex 
  or 
  left 
  valve, 
  is 
  founded 
  upon 
  an 
  

   imperfect 
  acquaintance 
  with 
  the 
  habits 
  of 
  the 
  oyster; 
  for 
  if 
  living 
  oys- 
  

   ters 
  are 
  thrown 
  into 
  the 
  water, 
  they 
  will 
  invariably 
  fall 
  upon 
  the 
  bottom 
  

   with 
  the 
  left 
  valve 
  downward. 
  If 
  dead 
  oyster-shells 
  (loose 
  valves) 
  be 
  

   similarly 
  thrown 
  into 
  the 
  water, 
  they 
  will 
  invariably 
  fall 
  with 
  the 
  hollow 
  

   side 
  up 
  and 
  the 
  convex 
  one 
  down. 
  And, 
  furthermore, 
  both 
  living 
  and 
  

   dead 
  oysters 
  remain 
  in 
  just 
  the 
  position 
  in 
  which 
  they 
  fall. 
  Dead 
  shells 
  

   sown 
  as 
  cultch 
  or 
  collectors 
  fall 
  in 
  such 
  a 
  position 
  and 
  most 
  of 
  the 
  spat 
  

   is 
  caught 
  on 
  the 
  exposed 
  parts 
  of 
  the 
  under 
  surface 
  only 
  of 
  such 
  shells, 
  

   whereas 
  little 
  is 
  found 
  to 
  grow 
  on 
  the 
  upper 
  surface. 
  The 
  reason 
  for 
  

   this 
  is, 
  that 
  the 
  sediment 
  which 
  is 
  deposited 
  on 
  the 
  upper 
  surfaces 
  as- 
  

   phyxiates 
  the 
  very 
  young 
  oyster-spat 
  and 
  other 
  larva? 
  which 
  affix 
  them- 
  

   selves 
  before 
  they 
  can 
  become 
  established 
  and 
  strong 
  enough 
  to 
  resist 
  

   its 
  effects. 
  The 
  affixed 
  organisms 
  on 
  the 
  exposed, 
  inclined 
  under 
  sur- 
  

   faces 
  of 
  the 
  shells 
  are, 
  on 
  the 
  other 
  hand, 
  protected 
  from 
  the 
  accumula- 
  

   tion 
  of 
  sediment. 
  

  

  It 
  is 
  also 
  well 
  known 
  that 
  the 
  right 
  valve 
  of 
  the 
  oyster 
  is 
  always 
  the 
  

   most 
  deeply 
  pigmented, 
  while 
  the 
  lower 
  or 
  left 
  one 
  is 
  paler. 
  This 
  is 
  al- 
  

   ways 
  the 
  case 
  when 
  oysters 
  lie 
  almost 
  flat 
  on 
  the 
  bottom. 
  When 
  crowd- 
  

   ed 
  together 
  on 
  the 
  natural 
  banks 
  on 
  a 
  vertical 
  position 
  there 
  is 
  less 
  dif- 
  

   ference 
  between 
  the 
  colors 
  of 
  the 
  valves. 
  This 
  difference 
  is 
  obviously 
  

   due 
  to 
  some 
  influence 
  exerted 
  by 
  the 
  position 
  of 
  the 
  aspects 
  of 
  the 
  body 
  

   of 
  the 
  animal 
  in 
  respect 
  to 
  the 
  light, 
  the 
  same 
  as 
  in 
  land 
  and 
  aquatic 
  ani- 
  

   mals 
  generally. 
  I 
  would 
  conclude, 
  for 
  this 
  last 
  reason 
  alone, 
  that 
  the 
  

   right 
  valve 
  of 
  the 
  oyster 
  is 
  normally 
  always 
  uppermost, 
  were 
  it 
  not 
  for 
  

   the 
  fact 
  that 
  I 
  have 
  observed 
  all 
  of 
  the 
  stages 
  of 
  transition 
  from 
  the 
  spat 
  

   to 
  the 
  adult 
  condition 
  in 
  confirmation 
  of 
  such 
  a 
  conclusion. 
  It 
  is 
  true 
  

   that 
  many 
  young 
  oysters 
  have 
  the 
  right 
  valve 
  looking 
  down 
  when 
  

   allowed 
  to 
  grow 
  upon 
  cultch 
  or 
  shells 
  which 
  have 
  been 
  sown 
  upon 
  the 
  

   bottom 
  to 
  favor 
  the 
  collection 
  of 
  the 
  spat, 
  ; 
  but 
  that 
  circumstance 
  by 
  no 
  

   means 
  invalidates, 
  as 
  supposed 
  rather 
  hastily 
  by 
  Mr. 
  Cunningham, 
  the 
  

   observations 
  and 
  conclusions 
  of 
  such 
  cautious 
  and 
  careful 
  investi- 
  

   gators 
  as 
  Brooks, 
  Woodward, 
  Jeffrey, 
  Huxley, 
  Horst, 
  and 
  others. 
  

  

  VII. 
  The 
  annual 
  set 
  of 
  spat 
  on 
  the 
  natural 
  banks 
  is 
  remark-ably 
  large. 
  

   In 
  fact, 
  upon 
  a 
  natural 
  bank 
  the 
  number 
  annually 
  removed 
  is 
  very 
  

  

  