﻿PROPAGATION 
  OF 
  FEESH-WATER 
  MUSSELS. 
  41 
  

  

  of 
  the 
  ordinary 
  type 
  in 
  the 
  Anodontmse 
  (see 
  pi. 
  iv, 
  fig. 
  27). 
  The 
  

   hook 
  has 
  the 
  character 
  of 
  a 
  straight 
  thong 
  inside 
  the 
  apex 
  of 
  each 
  

   valve. 
  The 
  glochidium 
  has 
  been 
  identified 
  as 
  that 
  of 
  Unio 
  cras- 
  

   sidens. 
  

  

  The 
  absence 
  of 
  evidence 
  of 
  natural 
  infections 
  from 
  certain 
  species 
  

   of 
  mussels 
  and 
  failure 
  to 
  obtain 
  infections 
  -wdth 
  them 
  according 
  to 
  

   known 
  methods 
  has 
  led 
  to 
  the 
  search 
  for 
  them 
  as 
  internal 
  parasites 
  

   of 
  fishes. 
  My 
  examination 
  of 
  the 
  alimentary 
  tract 
  of 
  fishes 
  has 
  

   given 
  negative 
  results 
  entirely. 
  Mr. 
  T. 
  Surber, 
  after 
  infecting 
  with 
  

   Quadrula 
  trigona, 
  found 
  their 
  glochidia 
  in 
  the 
  intestine 
  17 
  hours 
  later, 
  

   but 
  they 
  were 
  not 
  encysted, 
  and 
  the 
  supposition 
  was 
  that 
  they 
  were 
  

   not 
  established 
  in 
  any 
  way. 
  

  

  Type 
  of 
  cysts. 
  — 
  The 
  type 
  of 
  cyst 
  varies 
  in 
  different 
  cases, 
  and 
  the 
  

   question 
  arises 
  as 
  to 
  what 
  are 
  the 
  factors 
  that 
  determine 
  the 
  form 
  of 
  

   a 
  cyst. 
  In 
  artificial 
  infections 
  on 
  several 
  species 
  of 
  fi-;h 
  the 
  cyst 
  in 
  

   each 
  fish 
  will 
  vary 
  in 
  form 
  as 
  well 
  as 
  in 
  distribution 
  upon 
  the 
  gill 
  in 
  

   each 
  species, 
  and 
  again 
  infections 
  with 
  different 
  species 
  of 
  mussel 
  will 
  

   vary 
  in 
  the 
  same 
  species 
  of 
  fish. 
  That 
  is, 
  stimulus 
  and 
  reaction 
  vary 
  

   with 
  the 
  parasite 
  and 
  host. 
  This 
  is 
  perhaps 
  self-evident, 
  and 
  as 
  a 
  rule 
  

   differences 
  are 
  not 
  striking, 
  but 
  as 
  there 
  are 
  occasional 
  cases 
  of 
  maiked 
  

   peculiarity 
  in 
  cysts 
  their 
  consideration 
  may 
  be 
  of 
  interest. 
  In 
  the 
  

   discussion 
  of 
  Quadrula 
  ehena 
  I 
  have 
  described 
  the 
  relatively 
  large 
  

   cysts. 
  This 
  holds 
  for 
  the 
  natural 
  host, 
  Pomolobus 
  chrysocMoris, 
  as 
  

   well 
  as 
  for 
  artificial 
  infections 
  on 
  other 
  species. 
  The 
  large 
  glochidium 
  

   of 
  Q. 
  lieros 
  has 
  a 
  relatively 
  thin 
  cyst 
  in 
  gill 
  infections. 
  In 
  the 
  case 
  of 
  

   Q. 
  pustulosa 
  the 
  glochidium 
  is 
  usually 
  quite 
  deeply 
  imbedded, 
  but 
  

   the 
  cyst 
  does 
  not 
  markedly 
  change 
  the 
  contour 
  of 
  the 
  gill 
  filaments. 
  

   This 
  is 
  due 
  in 
  part 
  to 
  the 
  manner 
  of 
  unplantation 
  of 
  the 
  glochidium, 
  

   it 
  being 
  usually 
  attached 
  to 
  the 
  edge 
  of 
  the 
  broad 
  filament 
  in 
  the 
  

   catfish. 
  There 
  is 
  commonly 
  an 
  inset 
  of 
  the 
  cyst 
  (pi. 
  iii, 
  fig. 
  23) 
  that 
  

   seems 
  peculiar 
  to 
  this 
  form, 
  but 
  is 
  not 
  constant. 
  Abnormal 
  cysts 
  of 
  

   strange 
  forms 
  are 
  occasionally 
  found. 
  I 
  have 
  figured 
  one 
  of 
  these 
  

   (pi. 
  Ill, 
  fig. 
  20), 
  in 
  which 
  the 
  hypertrophied 
  tissue 
  is 
  more 
  extensive 
  

   than 
  usual 
  and 
  prolonged 
  into 
  fijigers 
  or 
  rays. 
  In 
  that 
  shown 
  in 
  

   figure 
  20 
  the 
  stimulation 
  of 
  the 
  glocliidia 
  implanted 
  at 
  the 
  base 
  of 
  the 
  

   folds 
  of 
  the 
  filament 
  affected 
  apparently 
  the 
  fundament 
  of 
  the 
  folds, 
  

   and 
  thus 
  we 
  have 
  a 
  number 
  of 
  new 
  folds 
  produced. 
  Studies 
  of 
  cyst 
  

   formation, 
  normal 
  and 
  abnormal, 
  sh©uld 
  have 
  a 
  practical 
  value 
  in 
  

   determining 
  the 
  conditions 
  governing 
  retention 
  of 
  glochidia. 
  

  

  Seasons 
  of 
  infection. 
  — 
  The 
  time 
  of 
  infection 
  must 
  of 
  course 
  be 
  

   limited 
  to 
  the 
  breeding 
  season 
  of 
  the 
  mussels, 
  but 
  as 
  the 
  period 
  of 
  

   breeding 
  covers 
  months 
  m 
  both 
  the 
  long 
  and 
  the 
  short 
  period 
  types, 
  

   the 
  more 
  exact 
  fixing 
  of 
  the 
  time 
  of 
  infection 
  may 
  be 
  important. 
  I 
  

   have 
  already 
  discussed 
  the 
  question 
  in 
  connection 
  with 
  Q. 
  heros, 
  as 
  to 
  

  

  