﻿PROPAGATION 
  OF 
  FRESH- 
  WATER 
  MUSSELS. 
  21 
  

  

  of 
  unsuitable 
  conditions 
  in 
  artificial 
  infection. 
  Some 
  indication 
  that 
  

   this 
  was 
  the 
  case 
  was 
  soon 
  obtained. 
  The 
  glochidia 
  would 
  attach 
  in 
  

   some 
  instances 
  and 
  not 
  in 
  others. 
  It 
  is 
  of 
  course 
  necessary 
  to 
  imitate 
  

   natural 
  conditions 
  as 
  closely 
  as 
  possible 
  as 
  to 
  temperature, 
  aeration, 
  

   light, 
  etc. 
  The 
  results 
  were 
  more 
  favorable 
  when 
  the 
  sun 
  was 
  out 
  

   than 
  during 
  cool, 
  cloudy 
  weather 
  and 
  apparently 
  better 
  in 
  sunlight 
  

   than 
  in 
  shade. 
  It 
  was 
  found 
  important 
  to 
  infect 
  as 
  soon 
  as 
  possible 
  

   the 
  same 
  day 
  after 
  securing 
  the 
  gravid 
  mussels, 
  as 
  this 
  species 
  will 
  

   abort 
  glochidia 
  soon 
  after 
  capture. 
  The 
  cause 
  is 
  supposed 
  to 
  be 
  that 
  

   the 
  lack 
  of 
  aeration 
  due 
  to 
  confinement 
  causes 
  the 
  animals 
  to 
  expel 
  

   the 
  glochidia 
  which 
  must 
  tend 
  to 
  interfere 
  with 
  respiration. 
  The 
  

   small 
  degree 
  of 
  special 
  differentiation 
  required 
  to 
  form 
  a 
  marsupium 
  

   and 
  the 
  presence 
  of 
  the 
  glochidia 
  in 
  all 
  four 
  gills 
  of 
  the 
  Quadrulas 
  

   undoubtedly 
  contribute 
  to 
  this. 
  

  

  Infection 
  and 
  encystment 
  of 
  the 
  glochidia 
  were 
  obtained. 
  (PI. 
  m, 
  

   fig. 
  24.) 
  The 
  latter 
  was 
  even 
  observed 
  under 
  the 
  microscope 
  upon 
  

   filaments 
  severed 
  from 
  the 
  gill 
  and 
  immersed 
  in 
  physiological 
  salt 
  

   solution. 
  In 
  one 
  case 
  observed 
  the 
  glochidium 
  was 
  completely 
  

   covered 
  by 
  the 
  encystment 
  in 
  four 
  hours. 
  

  

  In 
  the 
  case 
  of 
  the 
  fish 
  left 
  in 
  tanks 
  and 
  aquaria 
  the 
  glochidia, 
  

   although 
  well 
  encysted, 
  were 
  shed 
  in 
  from 
  one 
  to 
  three 
  days 
  in 
  all 
  

   cases. 
  Tlie 
  longest 
  retention 
  was 
  found 
  in 
  the 
  black 
  bass. 
  The 
  

   cysts 
  in 
  these 
  infections 
  were 
  exceedingly 
  large, 
  the 
  excessive 
  hyper- 
  

   trophy 
  apparently 
  being 
  due 
  to 
  excessive 
  stimulation. 
  (See 
  fig. 
  24.) 
  

  

  In 
  one 
  instance 
  the 
  fish 
  were 
  immersed 
  in 
  a 
  salt 
  bath 
  (NaCl, 
  10 
  per 
  

   cent) 
  before 
  introducing 
  them 
  to 
  the 
  container 
  holding 
  the 
  glochidia. 
  

   This 
  resulted 
  in 
  more 
  certain 
  and 
  rapid 
  infection 
  than 
  usual 
  in 
  all 
  

   species 
  experimented 
  upon, 
  but 
  the 
  infection 
  was 
  no 
  more 
  persistent. 
  

   The 
  significance 
  of 
  the 
  results 
  in 
  this 
  experiment 
  I 
  will 
  take 
  up 
  in 
  the 
  

   general 
  discussion. 
  

  

  After 
  the 
  completion 
  of 
  a 
  number 
  of 
  such 
  experiments 
  the 
  dis- 
  

   covery 
  was 
  made, 
  as 
  previously 
  mentioned, 
  of 
  infections 
  in 
  large 
  num- 
  

   bers 
  on 
  the 
  blue 
  herring, 
  indicating 
  it 
  as 
  the 
  host 
  fish 
  for 
  the 
  nigger- 
  

   head. 
  This 
  gave 
  an 
  explanation 
  of 
  the 
  inconclusive 
  results 
  already 
  

   attained, 
  but, 
  on 
  the 
  other 
  hand, 
  it 
  did 
  not 
  offer 
  ready 
  means 
  for 
  the 
  

   application 
  of 
  artificial 
  infection. 
  The 
  host 
  in 
  this 
  case 
  is 
  a 
  fish 
  

   which 
  offers 
  great 
  difficulties 
  to 
  the 
  methods 
  at 
  present 
  employed 
  in 
  

   artificial 
  propagation, 
  in 
  that 
  it 
  is 
  rarely 
  taken 
  here 
  and 
  is 
  difficult 
  

   to 
  retain 
  in 
  a 
  living 
  condition 
  long 
  enough 
  to 
  successfully 
  subject 
  it 
  to 
  

   infection. 
  In 
  order 
  to 
  find 
  how 
  to 
  do 
  this, 
  it 
  wiU 
  probably 
  be 
  neces- 
  

   sary 
  to 
  experiment 
  in 
  localities 
  where 
  both 
  the 
  fish 
  and 
  mussel 
  are 
  

   abundant. 
  If 
  possible 
  to 
  capture 
  in 
  pound 
  nets 
  or 
  traps 
  or 
  by 
  careful 
  

   handling 
  when 
  seined, 
  they 
  could 
  be 
  infected 
  without 
  removal 
  from 
  

   the 
  water. 
  As 
  the 
  mussel 
  is 
  a 
  species 
  found 
  in 
  the 
  larger 
  rivers, 
  in- 
  

   closures 
  would 
  have 
  to 
  be 
  made 
  in 
  a 
  body 
  of 
  water 
  having 
  a 
  current. 
  

  

  