﻿PROPAGATION 
  OP 
  FRESH-WATER 
  MUSSELS. 
  19 
  

  

  Since 
  finding 
  this 
  natural 
  infection 
  by 
  the 
  niggerhead, 
  Mr. 
  Surber 
  

   has 
  given 
  special 
  attention 
  to 
  the 
  investigation 
  of 
  the 
  infections 
  by 
  

   this 
  mussel 
  on 
  the 
  blue 
  herring. 
  (See 
  Surber, 
  1913.) 
  

  

  The 
  number 
  of 
  glochidia 
  on 
  a 
  single 
  fish 
  is 
  remarkable, 
  some 
  3,700 
  

   being 
  found 
  on 
  one, 
  well 
  encysted 
  and 
  giving 
  evidence 
  of 
  maturing 
  

   on 
  the 
  host. 
  This, 
  together 
  with 
  the 
  relatively 
  large 
  number 
  of 
  

   infected 
  fish 
  taken, 
  seems 
  to 
  fix 
  this 
  species 
  as 
  the 
  natural 
  host 
  of 
  

   the 
  niggerhead. 
  

  

  The 
  cases 
  of 
  infection 
  observed 
  on 
  the 
  black 
  bass 
  and 
  crappies 
  are 
  

   probably 
  either 
  accidental 
  infections 
  which 
  would 
  not 
  mature 
  or 
  they 
  

   are 
  the 
  very 
  similar 
  glochidia 
  of 
  the 
  pig- 
  toe, 
  Q. 
  trigona, 
  or 
  the 
  much 
  

   less 
  common 
  Q. 
  solida. 
  In 
  these 
  three 
  species 
  the 
  glochidia 
  are 
  so 
  

   much 
  alike 
  that 
  they 
  can 
  not 
  easily 
  be 
  distinguished 
  when 
  embedded 
  

   in 
  the 
  tissues 
  of 
  the 
  host, 
  especially 
  when 
  their 
  number 
  is 
  limited. 
  

   The 
  implantation 
  upon 
  this 
  fish 
  may 
  be 
  at 
  any 
  point 
  on 
  the 
  gill 
  fila- 
  

   ments, 
  but 
  shows 
  a 
  tendency 
  to 
  distribution 
  on 
  the 
  tips. 
  The 
  fila- 
  

   ments 
  are 
  so 
  small 
  that 
  several 
  are 
  involved 
  in 
  a 
  cyst, 
  which 
  is 
  usually 
  

   arge 
  for 
  the 
  size 
  of 
  the 
  glochidium, 
  as 
  observed 
  in 
  artificial 
  infections 
  

   with 
  this 
  glochidium 
  on 
  other 
  species 
  of 
  fish. 
  (See 
  artificial 
  infec- 
  

   tion, 
  p. 
  20.) 
  

  

  Several 
  glochidia 
  occur 
  in 
  a 
  common 
  or 
  compound 
  cyst 
  where 
  they 
  

   happen 
  to 
  attach 
  closely. 
  A 
  peculiarity 
  observable 
  in 
  many 
  prepara- 
  

   tions 
  is 
  the 
  presence 
  of 
  spaces 
  in 
  the 
  cysts 
  apparently 
  once 
  occupied 
  

   by 
  a 
  glochidium. 
  Adjacent 
  to 
  or 
  near 
  these 
  may 
  be 
  glochidia. 
  

   Surber 
  (1913) 
  has 
  interpreted 
  these 
  as 
  cases 
  of 
  migration 
  of 
  the 
  glo- 
  

   chidia. 
  This, 
  if 
  the 
  correct 
  interpretation, 
  is 
  a 
  condition 
  not 
  pre- 
  

   viously 
  observed. 
  I 
  am 
  not 
  yet 
  convinced 
  that 
  there 
  is 
  any 
  migration 
  

   except 
  that 
  necessary 
  in 
  escaping 
  from 
  the 
  cysts, 
  as 
  examples 
  may 
  

   be 
  seen 
  where 
  the 
  glochidium 
  has 
  a 
  well-defined 
  sheath 
  in 
  what 
  I 
  

   understand 
  Surber 
  would 
  consider 
  the 
  second 
  position. 
  

  

  Infections 
  on 
  the 
  blue 
  herring 
  during 
  the 
  remaining 
  season 
  were 
  

   found 
  most 
  abundant 
  in 
  August, 
  falUng 
  off 
  in 
  number 
  in 
  September, 
  

   the 
  latest 
  being 
  September 
  24 
  to 
  26, 
  when 
  2 
  out 
  of 
  9 
  were 
  found 
  

   infected. 
  My 
  latest 
  record 
  for 
  gravid 
  niggerheads 
  is 
  September 
  3, 
  

   3 
  gravid 
  out 
  of 
  63 
  examined. 
  The 
  difference 
  of 
  23 
  days 
  between 
  

   Sei)tember 
  3, 
  the 
  last 
  record 
  for 
  the 
  gravid 
  mussel, 
  and 
  the 
  26tli, 
  the 
  

   last 
  for 
  infected 
  fish, 
  as 
  a 
  rough 
  indication 
  of 
  length 
  of 
  the 
  parasitic 
  

   period, 
  would 
  signify 
  that 
  in 
  this 
  case 
  it 
  is 
  longer 
  than 
  in 
  the 
  case 
  of 
  

   the 
  warty-back, 
  Q. 
  yustulosa. 
  

  

  Reference 
  to 
  a 
  specimen 
  of 
  this 
  fish 
  taken 
  on 
  June 
  18, 
  1910, 
  by 
  

   H. 
  W. 
  Clark, 
  revealed 
  natural 
  infection 
  with 
  the 
  niggerhead. 
  This 
  

   is 
  the 
  earliest 
  season 
  date 
  that 
  I 
  know 
  for 
  an 
  infection, 
  but 
  corre- 
  

   sponds 
  with 
  our 
  records 
  of 
  5 
  gravid 
  mussels 
  on 
  May 
  31 
  and 
  13 
  on 
  

   June 
  17. 
  

  

  