﻿LOBSTER 
  AND 
  CLAM 
  INVESTIGATIONS. 
  209 
  

  

  It 
  is 
  not 
  clear 
  Avh}', 
  in 
  thi.s 
  case, 
  the 
  mature 
  clams 
  on 
  the 
  beach 
  above 
  

   the 
  low 
  tide 
  line 
  escaped, 
  though 
  the 
  water 
  iiowing 
  over 
  them 
  possibly 
  

   may 
  have 
  contained 
  sufficient 
  food 
  for 
  so 
  small 
  a 
  number, 
  and 
  the 
  con- 
  

   taminated 
  water 
  would 
  remain 
  largely 
  in 
  the 
  rapid 
  stream 
  over 
  the 
  

   lower 
  bed, 
  both 
  on 
  the 
  ebb 
  and 
  flood 
  tide. 
  A 
  number 
  were 
  found 
  

   dead, 
  and 
  the 
  beaches 
  were 
  dug 
  ver}- 
  little 
  by 
  clammers, 
  who 
  might 
  

   have 
  injured 
  many 
  so 
  as 
  subsequentl}^ 
  to 
  have 
  caused 
  their 
  death. 
  

   Very 
  likely 
  other 
  factors 
  not 
  observed 
  entered 
  into 
  the 
  extermination 
  

   of 
  the 
  small 
  clams. 
  

  

  VARIATION 
  OF 
  THE 
  SET 
  OF 
  DIFFERENT 
  YEARS. 
  

  

  Much 
  attention 
  has 
  been 
  given 
  to 
  the 
  production 
  of 
  oyster 
  seed. 
  In 
  

   Europe 
  and 
  in 
  the 
  United 
  States 
  it 
  has 
  been 
  found 
  that 
  the 
  produc- 
  

   tiveness 
  varied 
  greatl}^ 
  in 
  ditierent 
  seasons. 
  There 
  is 
  nothing 
  regular 
  

   about 
  it. 
  Favorable 
  and 
  unfavorable 
  seasons 
  may 
  alternate 
  for 
  a 
  time, 
  

   or 
  there 
  ma}^ 
  be 
  a 
  succession 
  of 
  productive 
  or 
  unproductive 
  j^ear.s. 
  

   Mobius" 
  says: 
  "In 
  1860 
  there 
  were 
  many 
  young 
  broods 
  upon 
  the 
  

   beds 
  near 
  the 
  island 
  of 
  Re 
  and 
  near 
  Rocher 
  d'Aire 
  and 
  but 
  few 
  broods 
  

   at 
  Arcachon; 
  1861 
  was 
  a 
  good 
  brood 
  year 
  for 
  all 
  three 
  places; 
  1862, 
  

   bad 
  for 
  the 
  island 
  of 
  Re 
  and 
  good 
  for 
  both 
  of 
  the 
  others, 
  and 
  in 
  1865 
  

   there 
  were 
  very 
  many 
  young 
  in 
  the 
  bay 
  of 
  Arcachon 
  and 
  but 
  few 
  near 
  

   Rocher 
  d'Aire 
  and 
  the 
  island 
  of 
  Re. 
  The 
  causes 
  of 
  these 
  variations 
  

   are 
  thus 
  local 
  in 
  their 
  action, 
  but 
  what 
  they 
  are 
  is 
  not 
  full}^ 
  known, 
  

   l)eyond 
  the 
  fact 
  that 
  a 
  definite 
  density 
  of 
  the 
  water 
  is 
  most 
  favora>>l'^ 
  

   for 
  egg 
  la^ang 
  in 
  the 
  European 
  oyster. 
  

  

  There 
  has 
  been 
  no 
  accurate 
  study 
  of 
  the 
  spawning 
  of 
  the 
  clam. 
  The 
  

   variation 
  in 
  the 
  size 
  of 
  the 
  set 
  is, 
  however, 
  much 
  like 
  that 
  of 
  the 
  oys- 
  

   ter. 
  While 
  the 
  young 
  in 
  1899 
  appeared 
  in 
  great 
  numbers 
  along 
  the 
  

   shores 
  of 
  Buzzards 
  and 
  Narragansett 
  bays, 
  in 
  1900 
  thej^ 
  were 
  very 
  

   scarce 
  in 
  both 
  localities. 
  At 
  Duxbury 
  and 
  Essex 
  the 
  set 
  was 
  said 
  to 
  

   be 
  favorable 
  in 
  1900. 
  These 
  places 
  are 
  north 
  of 
  Cape 
  Cod, 
  where 
  the 
  

   biological 
  conditions 
  are 
  very 
  difi'erent 
  from 
  those 
  on 
  the 
  south 
  side. 
  

   The 
  conditions 
  seem 
  to 
  be 
  local. 
  

  

  The 
  variation 
  of 
  the 
  set 
  nui}^ 
  be 
  due 
  to 
  the 
  fact 
  that 
  few 
  or 
  man}^ 
  

   ova 
  are 
  produced 
  at 
  different 
  times, 
  or 
  it 
  is 
  possible 
  that 
  eggs 
  are 
  

   always 
  abundant, 
  and 
  that 
  at 
  times 
  some 
  unknown 
  condition 
  prevents 
  

   the 
  swimming 
  embiyos 
  from 
  establishing 
  themselves 
  on 
  the 
  bottom. 
  

   It 
  is 
  not 
  yet 
  possible 
  to 
  sa}^ 
  what 
  efi'ect 
  the 
  degree 
  of 
  salinity 
  of 
  the 
  

   water 
  has 
  upon 
  the 
  production 
  of 
  the 
  sexual 
  elements 
  of 
  the 
  clam, 
  or 
  

   upon 
  the 
  development 
  of 
  the 
  embryo. 
  It 
  is 
  probabl}^ 
  little, 
  because, 
  

   unlike 
  the 
  oyster, 
  the 
  welfare 
  of 
  the 
  adult 
  clam 
  is 
  not 
  determined 
  b}^ 
  

   a 
  limited 
  and 
  definite 
  densit3\ 
  

  

  (I 
  Die 
  Auster 
  und 
  die 
  Austerwirthschaft. 
  Karl 
  Mobius. 
  U. 
  S. 
  Fish 
  Commission 
  Report 
  for 
  1880. 
  

   F. 
  C. 
  1903 
  14 
  

  

  