﻿26 
  PROPAGATION 
  OF 
  FRESH-WATER 
  MUSSELS. 
  

  

  introduced, 
  for 
  the 
  most 
  part, 
  probably 
  in 
  the 
  parasitic 
  stage 
  on 
  fish 
  

   retained 
  in 
  the 
  ponds. 
  As 
  the 
  first 
  example 
  of 
  the 
  Quadrula 
  group 
  

   raised 
  in 
  captivity, 
  it 
  has 
  interest 
  and 
  is 
  something 
  of 
  a 
  demonstration 
  

   that 
  they 
  may 
  be 
  raised 
  under 
  such 
  conditions. 
  This 
  was 
  the 
  fourth 
  

   most 
  abundant 
  species 
  in 
  my 
  collections 
  from 
  the 
  river." 
  

  

  Glochidium 
  (pi. 
  v, 
  fig. 
  32). 
  — 
  The 
  breeding 
  records 
  indicate 
  that 
  

   mature 
  glochidia 
  are 
  to 
  be 
  found 
  during 
  June, 
  July, 
  and 
  August. 
  

   On 
  June 
  26 
  I 
  observed 
  tne 
  spawning 
  of 
  this 
  species. 
  Tne 
  mussel 
  

   was 
  marooned 
  on 
  a 
  sand 
  bar 
  and 
  only 
  partly 
  in 
  the 
  water, 
  and 
  the 
  

   loose 
  white 
  mass 
  of 
  glochidia 
  were 
  collecting 
  in 
  a 
  depression 
  in 
  the 
  

   sand 
  behind 
  it. 
  I 
  suspect 
  this 
  was 
  not 
  perfectly 
  normal 
  spawning, 
  

   since 
  the 
  mussel 
  was 
  being 
  left 
  by 
  the 
  receding 
  water, 
  and 
  cases 
  of 
  

   abortion 
  of 
  glochidia 
  are 
  commonly 
  observed 
  in 
  the 
  Quadrulas 
  when 
  

   placed 
  under 
  conditions 
  unfavorable 
  for 
  oxygenation 
  in 
  the 
  gills. 
  

   The 
  glochidium 
  (pi. 
  v, 
  fig. 
  32) 
  is 
  of 
  the 
  bookless 
  type, 
  subsemi- 
  

   circular, 
  elongate, 
  and 
  white 
  in 
  color. 
  It 
  possesses 
  a 
  thread 
  gland 
  

   and 
  larval 
  thread 
  like 
  Q. 
  heros, 
  and 
  probably 
  the 
  same 
  will 
  be 
  found 
  

   in 
  all 
  the 
  other 
  members 
  of 
  the 
  Crenodonta 
  group 
  as 
  limited 
  by 
  

   Simpson 
  (1900). 
  The 
  gland 
  is 
  somewhat 
  different 
  in 
  appearance 
  

   from 
  that 
  in 
  Q. 
  heros. 
  The 
  turns 
  or 
  loops 
  of 
  the 
  spiral 
  are 
  of 
  about 
  

   the 
  same 
  number, 
  but 
  a 
  small 
  portion 
  of 
  what 
  may 
  be 
  designated 
  the 
  

   distal 
  end, 
  becomes 
  abruptly 
  two 
  to 
  three 
  times 
  broader 
  than 
  the 
  

   remainder. 
  This 
  larger 
  portion 
  begins 
  at 
  the 
  posterior 
  end 
  of 
  the 
  

   hinge 
  fine 
  and 
  on 
  reaching 
  the 
  anterior 
  side 
  of 
  the 
  adductor 
  muscle 
  

   curves 
  in 
  close 
  to 
  its 
  ventral 
  and 
  posterior 
  side. 
  The 
  contents 
  of 
  this 
  

   enlarged 
  portion 
  is 
  the 
  coiled 
  hyaline 
  thread 
  secreted 
  by 
  the 
  gland, 
  in 
  

   a 
  less 
  condensed 
  state 
  than 
  at 
  the 
  time 
  of 
  its 
  emergence 
  from 
  the 
  

   external 
  pore, 
  which 
  lies 
  on 
  the 
  posterior 
  side 
  of 
  the 
  adductor 
  muscle. 
  

  

  The 
  dimensions 
  of 
  the 
  glochidium 
  are: 
  Height, 
  0.195 
  mm. 
  to 
  

   0.215 
  mm.; 
  length, 
  0.185 
  mm. 
  to 
  0.200 
  mm. 
  

  

  Natural 
  infection. 
  — 
  Five 
  examples 
  of 
  natural 
  infection 
  with 
  this 
  

   species 
  were 
  obtained 
  during 
  June, 
  July, 
  and 
  August. 
  The 
  fish 
  

   were 
  all 
  crappies, 
  both 
  Pomoxis 
  annularis 
  and 
  sparoides 
  and 
  were 
  

   caught 
  chiefly 
  in 
  the 
  channel 
  of 
  the 
  Mississippi 
  on 
  or 
  near 
  mussel 
  

   beds 
  where 
  Q. 
  plicata 
  was 
  abundant. 
  Surber 
  (1913) 
  reports 
  two 
  

   cases, 
  one 
  on 
  S. 
  canadense 
  and 
  one 
  on 
  P. 
  annularis, 
  both 
  for 
  July 
  20. 
  

   In 
  determining 
  natural 
  infection 
  of 
  this 
  species 
  it 
  is 
  necessary 
  to 
  

   distinguish 
  it 
  from 
  the 
  glochidium 
  of 
  the 
  "spike" 
  mussel, 
  Unio 
  

   gibbosus 
  (Barnes), 
  as 
  the 
  latter 
  has 
  a 
  similar 
  form 
  and 
  dimensions, 
  

   and 
  it 
  apparently 
  infects 
  some 
  of 
  the 
  same 
  species 
  of 
  fish. 
  Typical 
  

   glochidia 
  dift'er 
  in 
  the 
  following 
  respects: 
  

  

  The 
  dimensions 
  in 
  U. 
  gibbosus 
  are: 
  Height, 
  0.208 
  mm. 
  to 
  0.220 
  mm. 
  ; 
  

   length, 
  0.190 
  mm. 
  to 
  0.208 
  mm. 
  The 
  hinge 
  line 
  is 
  proportionately 
  

  

  a 
  I 
  have 
  received 
  two 
  juveniles 
  of 
  this 
  specias 
  about 
  5 
  mm. 
  in 
  length, 
  possessing 
  a 
  well-defined 
  byssus. 
  

   This 
  material 
  was 
  collected 
  in 
  Lake 
  Feppin 
  by 
  Mr. 
  A. 
  F. 
  Shira. 
  

  

  