﻿12 
  

  

  GROWTH 
  AND 
  MIGRATIOlSr 
  OF 
  FEESH-WATER 
  MUSSELS. 
  

  

  and 
  gives 
  data 
  for 
  comparison 
  of 
  yearly 
  growth 
  and 
  summer 
  months. 
  

   The 
  average 
  yearly 
  growth 
  for 
  20 
  specimens 
  shown 
  in 
  table 
  2, 
  as 
  ^^ 
  ell 
  

   as 
  the 
  growth 
  for 
  three 
  summer 
  months 
  (85 
  days) 
  is 
  shown 
  below 
  : 
  

  

  1 
  Per 
  cent 
  of 
  aggregate 
  gain. 
  

  

  6 
  It 
  should 
  be 
  noted 
  in 
  this 
  comparison 
  that 
  the 
  1910 
  and 
  1911 
  summer 
  months 
  were 
  different 
  in 
  weather 
  

   conditions. 
  During 
  1910 
  there 
  were 
  no 
  rains 
  heavy 
  enough 
  to 
  raise 
  the 
  creek 
  and 
  wash 
  out 
  the 
  food 
  sup- 
  

   ply 
  of 
  micro-organisms, 
  while 
  in 
  1911 
  there 
  were 
  two 
  periods 
  of 
  high 
  water, 
  one 
  in 
  July 
  and 
  one 
  in 
  August. 
  

  

  Per 
  cent 
  of 
  gain 
  gives 
  a 
  truer 
  basis 
  for 
  this 
  kind 
  of 
  comparison 
  

  

  than 
  the 
  average 
  net 
  gain. 
  The 
  lack 
  of 
  conformity 
  in 
  the 
  height 
  

  

  averages, 
  when 
  compared 
  with 
  other 
  measurements, 
  is 
  doubtless 
  due 
  

  

  to 
  error 
  on 
  account 
  of 
  the 
  great 
  difficulty 
  in 
  getting 
  this 
  dimension 
  

  

  in 
  rapid 
  field 
  measurements 
  because 
  of 
  the 
  circular 
  ventral 
  margins 
  

  

  of 
  these 
  species. 
  

  

  Table 
  3. 
  — 
  Seasonal 
  Growth. 
  

  

  Wliile 
  table 
  2 
  has 
  given 
  some 
  good 
  data 
  concerning 
  seasonal 
  

   growth, 
  table 
  3 
  gives 
  more 
  detail 
  and 
  permits 
  a 
  more 
  exact 
  location 
  

   of 
  the 
  growth 
  periods. 
  Table 
  3 
  specimens 
  are 
  from 
  lot 
  F, 
  Chikaskia 
  

   River. 
  These 
  specimens 
  were 
  checked 
  up, 
  approximately, 
  at 
  the 
  

   third, 
  ninth, 
  and 
  twelfth 
  months 
  that 
  they 
  were 
  under 
  observation, 
  

   and 
  the 
  results 
  are 
  shown 
  by 
  successive 
  records. 
  The 
  initial 
  records 
  

   were 
  taken 
  June 
  23-28, 
  1910; 
  second, 
  September 
  26, 
  1910; 
  third, 
  

   April 
  11, 
  1911; 
  and 
  fourth, 
  June 
  20, 
  1911. 
  Only 
  the 
  weight 
  '^ 
  and 
  

   length 
  records 
  appear 
  in 
  this 
  table. 
  The 
  average 
  gain 
  for 
  the 
  dif- 
  

   ferent 
  periods 
  we 
  find 
  to 
  be 
  as 
  follows: 
  

  

  a 
  Some 
  observers 
  report 
  weight 
  measurements 
  subject 
  to 
  a 
  great 
  deal 
  of 
  variation. 
  In 
  this 
  investigation 
  

   I 
  have 
  always 
  kept 
  the 
  specimens 
  out 
  of 
  water 
  for 
  short 
  intervals 
  and 
  always 
  under 
  cover. 
  Under 
  these 
  

   conditions 
  I 
  have 
  found 
  weight 
  measures 
  very 
  satisfactory 
  and 
  stable 
  under 
  repeated 
  reweighings. 
  

  

  