﻿38 
  PROPAGATION 
  OF 
  FRESH-WATER 
  MUSSELS. 
  

  

  Some 
  of 
  the 
  mechanical 
  factors 
  in 
  immunity 
  mentioned 
  by 
  Lefevre 
  

   and 
  Curtis 
  were 
  such 
  as 
  configuration 
  of 
  mouth 
  parts, 
  texture 
  of 
  

   gills, 
  smaUness 
  of 
  gill 
  openings, 
  and 
  rapidity 
  of 
  fin 
  movements. 
  

   The 
  third 
  factor 
  which 
  I 
  suggest, 
  viz, 
  failure 
  of 
  glochidia 
  to 
  react, 
  

   was 
  observed 
  in 
  experiments 
  upon 
  the 
  niggerhead, 
  Q. 
  ebena, 
  and 
  the 
  

   warty-back, 
  Q. 
  pustulosa. 
  In 
  the 
  latter 
  case 
  the 
  glochidia 
  fastened 
  

   readily 
  upon 
  the 
  catfish, 
  but 
  not 
  upon 
  other 
  species 
  of 
  fish 
  upon 
  

   which 
  the 
  glochidia 
  of 
  the 
  mucket, 
  L. 
  ligamentina, 
  will 
  fasten 
  readily. 
  

   It 
  is 
  difficult 
  to 
  obtain 
  any 
  infection 
  with 
  the 
  glochidia 
  of 
  the 
  nigger- 
  

   head 
  upon 
  the 
  members 
  of 
  the 
  Centrarchidse; 
  however, 
  under 
  cer- 
  

   tain 
  circumstances 
  (see 
  the 
  next 
  topic) 
  they 
  will 
  take 
  hold 
  so 
  vigor- 
  

   ously 
  as 
  to 
  threaten 
  overinfection. 
  From 
  such 
  results 
  it 
  seems 
  not 
  

   improbable 
  that 
  the 
  tissues 
  or 
  blood 
  of 
  the 
  nonhost 
  possess 
  reactions 
  

   in 
  the 
  nature 
  of 
  antibodies, 
  precipitins, 
  and 
  other 
  immunizing 
  agents, 
  

   such 
  as 
  those 
  discovered 
  in 
  the 
  higher 
  vertebrates, 
  while 
  the 
  glocliidium 
  

   is 
  especially 
  adapted 
  to 
  the 
  reactions 
  of 
  the 
  appropriate 
  host. 
  

  

  Induced 
  susceptibility. 
  — 
  I 
  have 
  already 
  mentioned, 
  in 
  discussing 
  

   the 
  niggerhead, 
  an 
  experiment 
  in 
  which 
  fish 
  were 
  immersed 
  in 
  a 
  

   solution 
  of 
  common 
  salt 
  (10 
  per 
  cent, 
  by 
  weight) 
  before 
  placing 
  in 
  

   the 
  i], 
  fee 
  ting 
  tank, 
  where 
  it 
  was 
  shown 
  that 
  this 
  treatme? 
  t 
  had 
  the 
  

   marked 
  efl'ect 
  of 
  causing 
  rapid 
  infection 
  where 
  previously 
  it 
  had 
  been 
  

   difficult 
  to 
  obtain. 
  We 
  have 
  here 
  possibly 
  a 
  suggestion 
  that 
  this 
  

   reaction 
  is 
  related 
  to 
  the 
  normal 
  habit 
  of 
  the 
  glocliidium 
  ia 
  respond- 
  

   ing 
  to 
  the 
  presence 
  of 
  its 
  natural 
  host, 
  the 
  blue 
  herring, 
  a 
  fish 
  reported 
  

   from 
  salt 
  water 
  and 
  possibly 
  anadromous. 
  However, 
  one 
  would 
  as- 
  

   sume 
  that 
  all 
  perceptible 
  traces 
  of 
  the 
  more 
  sahne 
  medium 
  would 
  be 
  

   lost 
  when 
  the 
  fish 
  had 
  passed 
  through 
  a 
  few 
  miles 
  of 
  fresh 
  water. 
  In 
  

   my 
  opinion, 
  there 
  is 
  no 
  causal 
  connection 
  here, 
  since 
  glochidia 
  of 
  many 
  

   species 
  show 
  excitement 
  in 
  the 
  presence 
  of 
  sodium 
  chloride 
  and 
  other 
  

   salts. 
  This 
  is 
  due 
  undoubtedly 
  to 
  the 
  fact 
  that 
  their 
  normal 
  reac- 
  

   tion 
  is 
  to 
  chemical 
  stimulation 
  from 
  the 
  ions 
  of 
  protoplasmic 
  salts 
  

   diff'used 
  from 
  the 
  animal 
  fluids 
  of 
  fishes' 
  gills 
  or 
  bodies. 
  As 
  the 
  glo- 
  

   chidia 
  did 
  not 
  remain 
  upon 
  the 
  fish 
  through 
  the 
  parasitic 
  period, 
  a 
  

   probable 
  explanation 
  would 
  be 
  that 
  the 
  salt 
  could 
  have 
  had 
  only 
  the 
  

   effect 
  of 
  overcoming 
  the 
  inhibition 
  of 
  the 
  glochidia 
  to 
  react. 
  

  

  The 
  effects 
  of 
  the 
  parasitism 
  of 
  the 
  glochidium 
  upon 
  the 
  host 
  and 
  

   the 
  exact 
  relations 
  to 
  the 
  host 
  at 
  various 
  stages 
  in 
  the 
  developi?ig 
  

   mussel 
  are 
  matters 
  the 
  investigation 
  of 
  which 
  should 
  be 
  productive 
  

   of 
  interesting 
  results. 
  Lefevre 
  and 
  Curtis 
  (1912) 
  record 
  observations 
  

   of 
  the 
  ingestion 
  of 
  portions 
  of 
  the 
  host's 
  tissues 
  by 
  the 
  glochidium 
  

   soon 
  after 
  implantation. 
  It 
  is 
  a 
  question 
  whether 
  the 
  host 
  con- 
  

   tinues 
  to 
  supply 
  sustenance 
  other 
  than 
  ox5^gen 
  in 
  forms 
  like 
  Lampsilis 
  

   ligamentina, 
  which 
  show 
  little 
  or 
  no 
  increase 
  in 
  size. 
  In 
  forms 
  like 
  

   those 
  of 
  the 
  Proptera 
  (Ortmann) 
  group, 
  which 
  increase 
  to 
  a 
  consid- 
  

   erable 
  extent 
  in 
  the 
  parasitic 
  stage 
  (see 
  metamorphosis 
  during 
  the 
  

  

  