﻿24 
  PEOPAGATION 
  OF 
  FEESH-WATER 
  MUSSELS. 
  

  

  tending 
  the 
  known 
  breeding 
  period 
  well 
  on 
  into 
  wSeptember. 
  In 
  July 
  

   I 
  took 
  a 
  gravid 
  example 
  only 
  30 
  mm. 
  in 
  length; 
  this 
  surprisingly 
  

   small 
  size 
  for 
  breeding 
  indicates 
  the 
  early 
  attainment 
  of 
  the 
  adult 
  

   stage. 
  The 
  glochidial 
  shell 
  of 
  this 
  species 
  seems 
  thin 
  and 
  more 
  deli- 
  

   cate 
  than 
  in 
  Q. 
  ehena. 
  The 
  eggs 
  are 
  a 
  pinkish 
  red, 
  the 
  glochidia 
  

   colorless, 
  filling 
  moderately 
  all 
  four 
  gills. 
  Unfertilized 
  eggs 
  were 
  

   found 
  with 
  glochidia, 
  so 
  that 
  gravid 
  mussels 
  have 
  gills 
  varying 
  in 
  

   color 
  from 
  a 
  deep 
  to 
  a 
  light 
  shade, 
  according 
  to 
  the 
  number 
  of 
  eggs 
  

   remaining 
  undeveloped. 
  The 
  number 
  of 
  undeveloped 
  eggs 
  is 
  sur- 
  

   prisingly 
  high, 
  sometimes 
  more 
  than 
  75 
  per 
  cent. 
  The 
  form 
  of 
  the 
  

   glochidium 
  is 
  of 
  the 
  subsemicircular 
  type 
  (fig. 
  33). 
  

  

  Dimensions: 
  Height, 
  0.136 
  mm. 
  to 
  0.149 
  mm.; 
  length, 
  0.136 
  mm. 
  

   to 
  0.153 
  mm. 
  The 
  smaller 
  size 
  and 
  straighter 
  lines 
  of 
  the 
  anterior 
  

   and 
  posterior 
  edges 
  of 
  the 
  shell 
  should 
  distinguish 
  this 
  glochidium 
  

   from 
  the 
  similar 
  glochidia 
  of 
  Q. 
  ehena 
  and 
  Q. 
  solida. 
  

  

  Natural 
  infection.— 
  The 
  natural 
  host 
  for 
  Q. 
  trigona 
  has 
  not 
  to 
  my 
  

   knowledge 
  been 
  determined 
  with 
  any 
  satisfactory 
  degree 
  of 
  certainty. 
  

   I 
  secured 
  infections 
  on 
  Pomoxis 
  sparoides 
  August 
  2 
  and 
  Pomoxis 
  

   annularis 
  August 
  9, 
  observing 
  in 
  the 
  first 
  2 
  and 
  the 
  second 
  4 
  glochidia 
  

   which 
  answer 
  to 
  the 
  dimensions 
  of 
  Q. 
  trigona; 
  but 
  as 
  unmistakable 
  

   preparations 
  of 
  these 
  were 
  not 
  obtained 
  it 
  is 
  not 
  at 
  present 
  possible 
  

   to 
  state 
  whether 
  they 
  may 
  not 
  be 
  either 
  Quadrula 
  solida 
  or 
  Q. 
  ehena. 
  

   Since 
  the 
  host-fish 
  for 
  the 
  latter 
  has 
  been 
  pretty 
  definitely 
  determined 
  

   to 
  be 
  Pomolohus, 
  it 
  might 
  be 
  excluded 
  as 
  a 
  possibility 
  here 
  if 
  it 
  were 
  

   not 
  known 
  that 
  accidental 
  and 
  sporadic 
  infections 
  are 
  possible 
  on 
  

   other 
  than 
  the 
  usual 
  host. 
  A 
  single 
  case 
  is 
  reported 
  as 
  Q. 
  trigona 
  

   on 
  the 
  black 
  crappie, 
  P. 
  Sparoides, 
  by 
  Surber 
  (1913); 
  he 
  also 
  reports 
  

   an 
  infection 
  upon 
  Pomoxis 
  annularis, 
  but 
  thinlcs 
  both 
  of 
  these 
  may 
  

   be 
  accidental 
  infections. 
  Some 
  evidence 
  as 
  to 
  the 
  natural 
  host 
  was 
  

   obtained 
  in 
  the 
  finding 
  of 
  the 
  juvenile 
  of 
  this 
  species 
  in 
  an 
  arti- 
  

   ficial 
  pond 
  in 
  wliich 
  sunfish, 
  crappie, 
  and 
  gizzard 
  shad, 
  Dorosoma 
  

   cepedianum, 
  had 
  been 
  kept. 
  Since 
  gizzard 
  shad 
  have 
  not 
  been 
  

   found 
  with 
  gill 
  infections, 
  the 
  evidence 
  favors 
  the 
  sunfish 
  and 
  crappie 
  

   in 
  this 
  instance. 
  Further 
  evidence 
  was 
  obtained 
  in 
  the 
  successful 
  

   implantation 
  of 
  the 
  glochidia 
  on 
  the 
  gills 
  of 
  the 
  sunfish 
  in 
  artificial 
  

   infection; 
  this 
  will 
  be 
  taken 
  up 
  in 
  the 
  next 
  topic. 
  

  

  The 
  character 
  of 
  the 
  distribution 
  of 
  the 
  juveniles 
  of 
  Q. 
  trigona 
  must 
  

   be 
  of 
  some 
  significance; 
  it 
  was 
  found 
  to 
  be 
  the 
  most 
  generally 
  dis- 
  

   tributed 
  of 
  all 
  species 
  in 
  explorations 
  of 
  the 
  river 
  bottom, 
  from 
  which 
  

   it 
  is 
  a 
  safe 
  presumption 
  that 
  the 
  host 
  must 
  be 
  a 
  common 
  fish. 
  To 
  

   summarize 
  the 
  results, 
  the 
  evidence, 
  though 
  not 
  conclusive, 
  points 
  to 
  

   the 
  sunfish 
  and 
  crappie 
  as 
  the 
  hosts. 
  

  

  Artificial 
  infection. 
  — 
  In 
  my 
  experiments 
  with 
  this 
  mussel 
  five 
  

   species 
  of 
  fish 
  were 
  tested, 
  Micropterus 
  salmoides, 
  Lepomis 
  pallidus, 
  

   Eupomotis 
  gihhosus, 
  Pomoxis 
  sparoides, 
  and 
  P. 
  annulai%s. 
  Examina- 
  

  

  