﻿44 
  PROPAGATION 
  OF 
  FEESH-WATER 
  MUSSELS. 
  

  

  seem 
  to 
  indicate 
  that 
  its 
  function 
  later 
  is 
  not 
  of 
  a 
  fundamental 
  nature 
  

   ]ike 
  excretion 
  or 
  it 
  would 
  persist 
  in 
  all. 
  Lefevre 
  and 
  Curtis 
  advance 
  

   the 
  argument 
  that 
  the 
  threads 
  are 
  dissolved 
  in 
  a 
  day 
  or 
  two 
  and 
  so 
  

   are 
  not 
  effective 
  during 
  the 
  greater 
  part 
  of 
  the 
  period 
  in 
  which 
  the 
  

   glochidia 
  may 
  be 
  on 
  the 
  bottom. 
  This 
  would 
  make 
  no 
  difference 
  if 
  

   infections 
  take 
  place 
  at 
  the 
  time 
  the 
  glochidia 
  leave 
  the 
  mussel, 
  the 
  

   evidence 
  for 
  which 
  I 
  have 
  discussed 
  above. 
  (See 
  conditions 
  of 
  

   infection 
  in 
  nature, 
  p. 
  39.) 
  

  

  Absence 
  of 
  'parasitism. 
  — 
  The 
  interesting 
  discovery 
  of 
  metamor- 
  

   phosis 
  without 
  parasitism 
  as 
  reported 
  by 
  Lefevre 
  and 
  Curtis 
  (1912) 
  

   for 
  StropMtus 
  edentulus 
  (Sa}^ 
  suggests 
  the 
  possibility 
  of 
  some 
  similar 
  

   explanation 
  for 
  the 
  absence 
  of 
  evidence 
  of 
  infection 
  by 
  some 
  common 
  

   species. 
  This 
  is 
  especially 
  to 
  be 
  looked 
  for 
  in 
  species 
  which 
  have 
  

   conglutinates 
  similar 
  in 
  character 
  to 
  those 
  of 
  S. 
  edentulus. 
  I 
  have 
  

   in 
  mind 
  those 
  of 
  Obliquaria 
  reiiexa 
  (Rafinesque). 
  Tlie 
  fact 
  that 
  

   infections 
  of 
  this 
  species 
  have 
  not 
  been 
  found 
  lends 
  support 
  to 
  the 
  

   supposition 
  that 
  there 
  is 
  possibly 
  something 
  unusual 
  in 
  their 
  life 
  

   history. 
  

  

  Another 
  species 
  of 
  mussel 
  for 
  which 
  no 
  natural 
  infections 
  have 
  been 
  

   reported 
  is 
  Anodonta 
  imbecilUs. 
  While 
  making 
  measurements 
  of 
  the 
  

   glochidia 
  from 
  a 
  number 
  of 
  gravid 
  individuals 
  of 
  this 
  species 
  collected 
  

   during 
  the 
  month 
  of 
  November, 
  I 
  noticed 
  that 
  in 
  many 
  cases 
  what 
  I 
  

   had 
  supposed 
  at 
  first 
  glance 
  were 
  mature 
  glochidia 
  were 
  in 
  fact 
  

   juvenile 
  mussels 
  with 
  organs 
  developed 
  to 
  the 
  stage 
  usually 
  seen 
  in 
  

   juveniles 
  at 
  the 
  time 
  they 
  leave 
  their 
  host. 
  These 
  young 
  mussels 
  he 
  

   crowded 
  in 
  the 
  marsupial 
  gills 
  of 
  the 
  parent 
  without 
  any 
  conglutinate 
  

   structure 
  whatever. 
  The 
  outer 
  gi^ls, 
  as 
  in 
  other 
  anodontas, 
  are 
  

   marsupial, 
  and 
  these 
  become 
  well 
  distended 
  throughout 
  their 
  whole 
  

   length 
  when 
  gravid. 
  

  

  In 
  regard 
  to 
  the 
  breeding 
  of 
  this 
  species, 
  Ortmann 
  (1912) 
  says 
  it 
  is 
  

   gravid 
  from 
  September 
  to 
  May. 
  My 
  observations, 
  which 
  are 
  rather 
  

   limited, 
  I 
  give 
  below: 
  

  

  Fairport, 
  Iowa, 
  July 
  16, 
  1910, 
  1 
  with 
  glochidia. 
  

   Fairport, 
  Iowa, 
  May 
  13, 
  1912, 
  1 
  with 
  glochidia. 
  

   Fairport, 
  Iowa, 
  May 
  27, 
  1912, 
  1 
  with 
  early 
  embryos. 
  

   Moline, 
  111., 
  September 
  24, 
  1912, 
  1 
  not 
  gra\-id. 
  

  

  Moline, 
  111., 
  November 
  7, 
  1913, 
  2 
  with 
  early 
  embryos; 
  1 
  with 
  both 
  late 
  embryos 
  and 
  

   glochidia, 
  and 
  6 
  with 
  juveniles. 
  

  

  In 
  addition 
  to 
  these 
  I 
  have 
  found 
  numbers 
  of 
  free 
  juveniles 
  ranging 
  

   from 
  5 
  to 
  30 
  millimetere 
  not 
  sexually 
  mature. 
  These 
  stages 
  are 
  

   remarkable 
  for 
  the 
  thinness 
  of 
  their 
  shells 
  and 
  the 
  flatness 
  of 
  the 
  

   mussel 
  as 
  a 
  whole. 
  The 
  term 
  "floater" 
  of 
  the 
  mussel 
  fishermen 
  for 
  

   this 
  type 
  of 
  mussel 
  is 
  well 
  apphed 
  in 
  its 
  use 
  for 
  this 
  species. 
  

  

  The 
  presence 
  of 
  juveniles 
  during 
  November 
  in 
  the 
  gills 
  of 
  a 
  majority 
  

   of 
  the 
  specimens 
  examined 
  seems 
  to 
  indicate 
  that 
  metamorphosis 
  is 
  

  

  