﻿22 
  GROWTH 
  AND 
  MIGRATION 
  OF 
  FRESH-WATER 
  MUSSELS. 
  

  

  The 
  distribution 
  of 
  mussels 
  within 
  individual 
  streams, 
  and 
  in 
  the 
  

   Chikaskia 
  in 
  particular, 
  is 
  not 
  easy 
  to 
  explain. 
  Little 
  or 
  neghgible 
  

   migration 
  among 
  the 
  Quadrula3, 
  at 
  least, 
  lias 
  not 
  cleared 
  the 
  situation. 
  

  

  SUMMARY. 
  

  

  1. 
  Rate 
  of 
  growth 
  is 
  exceedingly 
  varial)le 
  for 
  individuals 
  of 
  a 
  single 
  

   species 
  in 
  the 
  same 
  stream 
  and 
  in 
  different 
  streams, 
  depending, 
  as 
  in 
  

   other 
  invertebrates, 
  upon 
  season, 
  food, 
  oxygen 
  supply, 
  and 
  other 
  con- 
  

   ditions. 
  Juvenile 
  mussels 
  grow 
  much 
  more 
  rapidly 
  than 
  adult 
  or 
  

   near-adult 
  individuals. 
  Lampsilis 
  species 
  grow 
  very 
  much 
  faster 
  

   than 
  Quadrulse. 
  Specimens 
  in 
  stable 
  conditions 
  seem 
  to 
  have 
  a 
  

   faii'ly 
  definite 
  rate 
  of 
  growth 
  from 
  year 
  to 
  year. 
  The 
  rate, 
  after 
  

   sexual 
  maturity, 
  is 
  slowed 
  down, 
  but 
  growth 
  goes 
  on 
  steadily, 
  though 
  

   the 
  proportional 
  increase 
  in 
  length 
  is 
  so 
  slow 
  as 
  to 
  make 
  appreciable 
  

   additions 
  very 
  slight, 
  so 
  that 
  growth 
  lines 
  in 
  Quadrulge, 
  after 
  a 
  size 
  

   of 
  100 
  millimeters 
  (4 
  inches) 
  has 
  been 
  reached, 
  can 
  not 
  be 
  ascer- 
  

   tamed 
  by 
  inspection. 
  

  

  2. 
  From 
  April 
  to 
  September 
  may 
  be 
  designated 
  as 
  growth 
  months, 
  

   most 
  specimens 
  showing 
  very 
  slight 
  increase 
  during 
  winter. 
  

  

  3. 
  Lines 
  of 
  arrested 
  growth 
  may 
  be 
  called 
  rest 
  rings, 
  the 
  conspicu- 
  

   ous 
  ones 
  bemg 
  usually 
  winter 
  rest 
  rings; 
  very 
  often, 
  however, 
  the 
  

   rings 
  may 
  be 
  two 
  or 
  more 
  years 
  apart, 
  or 
  several 
  equally 
  prominent 
  

   rings 
  may 
  be 
  formed 
  in 
  one 
  year. 
  Promment 
  lines 
  are 
  generally 
  due 
  

   to 
  double 
  prismatic 
  and 
  double 
  epidermal 
  layers. 
  Winter 
  rings, 
  es- 
  

   pecially 
  where 
  environmental 
  conditions 
  are 
  stable, 
  are 
  usually 
  suffi- 
  

  

  * 
  ciently 
  regular 
  for 
  use 
  as 
  indicators 
  of 
  age 
  in 
  estimating 
  roughly 
  the 
  

   time 
  required 
  for 
  a 
  commercial 
  species 
  to 
  reach 
  marketable 
  size. 
  

  

  4. 
  Under 
  favorable 
  conditions 
  there 
  is 
  little 
  migration 
  among 
  the 
  

   Quadrulse. 
  Some 
  of 
  the 
  Lampsiles 
  and 
  other 
  light-shelled 
  species 
  

   move 
  about 
  quite 
  actively, 
  but 
  probably 
  seldom 
  migrate 
  far 
  from 
  the 
  

   point 
  where 
  they 
  were 
  dropped 
  from 
  the 
  fish, 
  although 
  their 
  total 
  wan- 
  

   derings 
  may 
  be 
  considerable. 
  Water 
  of 
  sufficient 
  depth 
  is 
  essential 
  

   to 
  optimum 
  conditions. 
  The 
  minimum 
  depth 
  seems 
  to 
  be 
  at 
  least 
  2 
  

   feet; 
  the 
  range 
  up 
  to 
  the 
  maximum 
  has 
  not 
  been 
  studied. 
  Quadrulse 
  

   prefer 
  water 
  over 
  2 
  feet 
  deep. 
  The 
  reason 
  they 
  are 
  found 
  on 
  the 
  

   shoals 
  in 
  many 
  of 
  our 
  streams 
  may 
  be 
  explained 
  as 
  chance 
  distribu- 
  

   tion, 
  due 
  probably 
  to 
  the 
  fact 
  that 
  the 
  particular 
  individuals 
  have 
  

   never 
  found 
  optimum 
  conditions 
  after 
  their 
  parasitic 
  development, 
  

   and 
  the 
  reason 
  they 
  move 
  about 
  is 
  that 
  they 
  do 
  not 
  find 
  the 
  right 
  

  

  environment. 
  

  

  LITERATURE 
  CITED." 
  

  

  CoKER, 
  R. 
  E., 
  and 
  Surber, 
  T. 
  

  

  1911. 
  A 
  nole 
  on 
  the 
  metamorphosis 
  o£ 
  the 
  mussel 
  Lampsilis 
  Isevissimus. 
  Bio- 
  

   logical 
  Bulletin 
  of 
  the 
  Marine 
  Biological 
  Laboratory, 
  Woods 
  Hole, 
  Mass., 
  

   vol. 
  20, 
  p. 
  179-182, 
  1 
  pi. 
  

  

  a 
  Dr. 
  A. 
  E. 
  Ortmann 
  and 
  Dr. 
  F. 
  Haas 
  have 
  called 
  my 
  attention 
  to 
  Dr. 
  Haas's 
  monograph, 
  "Die 
  Union- 
  

   idae 
  in 
  Martini-Chemnitches 
  ConchyUeneabinet," 
  1910. 
  T 
  have 
  not 
  had 
  access 
  to 
  this 
  paper. 
  

  

  