﻿EXPERIMENTAL 
  STUDY 
  OF 
  THE 
  GROWTH 
  AND 
  

   MIGRATION 
  OF 
  FRESH-WATER 
  MUSSELS. 
  

  

  By 
  Frederick 
  B. 
  Isely, 
  

   Professor 
  of 
  Biology 
  , 
  Central 
  College, 
  Fayette. 
  Missouri. 
  

  

  INTRODUCTION. 
  

  

  The 
  growth 
  lines 
  of 
  the 
  Unionidae 
  have 
  long 
  been 
  considered 
  by 
  

   many 
  observers 
  as 
  *' 
  annual 
  rings," 
  marking 
  the 
  yearly 
  mcrease 
  m 
  the 
  

   shell 
  diameter. 
  On 
  the 
  other 
  hand, 
  proof 
  of 
  the 
  correctness 
  of 
  this 
  

   assumption 
  has 
  been 
  lacking, 
  and 
  not 
  a 
  few 
  investigators 
  have 
  ques- 
  

   tioned 
  its 
  validity. 
  

  

  If 
  the 
  so-called 
  annual 
  rings 
  do 
  mark 
  yearly 
  additions, 
  the 
  rate 
  

   of 
  growth 
  may 
  readily 
  be 
  ascertained 
  in 
  many 
  species 
  by 
  inspection; 
  

   if, 
  however, 
  two 
  or 
  three 
  of 
  these 
  lines 
  appear 
  m 
  one 
  season, 
  or 
  

   prominent 
  lines 
  appear 
  only 
  at 
  iiTegular 
  yearly 
  intervals, 
  the 
  impor- 
  

   tance 
  of 
  ''growth 
  Imes" 
  as 
  definite 
  indiodtors 
  of 
  rate 
  of 
  growth 
  loses 
  

   much 
  of 
  its 
  significance. 
  

  

  The 
  economic 
  importance 
  of 
  fresh-water 
  mussels 
  has 
  added 
  a 
  new 
  

   stimulus 
  to 
  the 
  study 
  of 
  the 
  growth 
  problem. 
  Investigations 
  <* 
  

   under 
  direction 
  of 
  the 
  Bureau 
  of 
  Fisheries 
  during 
  the 
  past 
  five 
  years 
  

   concerning 
  various 
  phases 
  of 
  and 
  questions 
  related 
  to 
  the 
  problem 
  

   of 
  artificial 
  propagation 
  of 
  the 
  species 
  valuable 
  for 
  use 
  m 
  the 
  manufac- 
  

   ture 
  of 
  pearl 
  buttons, 
  knife 
  handles, 
  etc., 
  has 
  promoted 
  inquuy 
  con- 
  

   cerning 
  the 
  time 
  required 
  for 
  an 
  economic 
  species 
  to 
  reach 
  marketable 
  

   size. 
  

  

  Israel 
  and 
  Haas, 
  among 
  German 
  mvestigators, 
  have 
  recently 
  given 
  

   the 
  growth 
  question 
  some 
  attention 
  in 
  connection 
  with 
  their 
  extensive 
  

   study 
  of 
  the 
  fresh-water 
  mussels 
  of 
  streams 
  of 
  Germany. 
  In 
  this 
  

   country 
  Lefevre, 
  Curtis, 
  and 
  Coker'' 
  have 
  gathered 
  experimental 
  

   data 
  concerning 
  growth. 
  

  

  In 
  my 
  study 
  of 
  the 
  ecology 
  of 
  the 
  Unionidas 
  durmg 
  the 
  past 
  five 
  

   years, 
  one 
  of 
  the 
  perplexuig 
  problems 
  has 
  been 
  the 
  rate 
  of 
  growth 
  and 
  

  

  a 
  Various 
  papers 
  by 
  Lefevre, 
  Curtis, 
  Coker, 
  and 
  other 
  workers, 
  in 
  Bureau 
  of 
  Fisheries 
  publications, 
  the 
  

   Journal 
  of 
  Experimental 
  Zoology, 
  and 
  the 
  Biological 
  Bulletin 
  for 
  1909, 
  1910, 
  1911, 
  and 
  1912. 
  

  

  b 
  Through 
  the 
  kindness 
  of 
  Dr. 
  Coker, 
  I 
  have 
  been 
  permitted 
  to 
  read 
  in 
  manuscript 
  the 
  results 
  of 
  liis 
  

   experiments 
  and 
  observations. 
  

  

  5 
  

  

  