﻿30 
  PROPAGATION 
  OF 
  FRESH-WATER 
  MUSSELS. 
  

  

  The 
  above 
  is 
  sufficiently 
  accurate 
  as 
  to 
  the 
  features 
  described 
  but 
  

   is 
  not 
  enough 
  to 
  identify 
  the 
  glochidium, 
  since 
  there 
  are 
  so 
  many 
  

   forms 
  answering 
  this 
  description. 
  I 
  think 
  the 
  following 
  will 
  serve 
  to 
  

   distinguish 
  it: 
  

  

  Dimensions: 
  Height, 
  0.316 
  mm. 
  to 
  0.340 
  mm.; 
  length, 
  0.250 
  mm. 
  

   to 
  0.260 
  mm. 
  The 
  right 
  valve 
  contains 
  a 
  large 
  and 
  conspicuous 
  

   thread 
  gland; 
  this 
  is 
  in 
  the 
  form 
  of 
  a 
  spiral 
  rod 
  (pi. 
  3, 
  fig. 
  21) 
  tapering 
  

   at 
  each 
  end, 
  and 
  having 
  about 
  two 
  turns 
  about 
  the 
  adductor 
  muscle. 
  

   As 
  compared 
  with 
  this 
  gland 
  in 
  Anodontas, 
  it 
  is 
  more 
  conspicuous 
  

   because 
  of 
  its 
  greater 
  width 
  and 
  its 
  being 
  possibly 
  more 
  highly 
  

   refractive 
  to 
  liglit. 
  The 
  inconspicuous 
  tapered 
  extremities 
  lie 
  near 
  

   the 
  ventral 
  side 
  of 
  the 
  adductor 
  muscle 
  and 
  one 
  of 
  them 
  opens 
  to 
  the 
  

   mantle 
  cavity; 
  from 
  this 
  opening 
  the 
  larval 
  thread 
  extends. 
  The 
  

   latter 
  is 
  of 
  considerable 
  length 
  and 
  lies 
  coiled 
  in 
  the 
  mantle 
  chamber. 
  

   It 
  consists 
  of 
  a 
  delicate 
  hyaline 
  thread 
  which 
  becomes 
  readily 
  extended 
  

   when 
  the 
  glochidia 
  are 
  extruded 
  from 
  the 
  parent 
  gills. 
  The 
  presence 
  

   of 
  a 
  thread 
  gland 
  has 
  not 
  been 
  previously 
  reported 
  for 
  the 
  Quadrula 
  

   group, 
  I 
  believe, 
  and 
  only 
  in 
  the 
  Anodontas 
  and 
  the 
  TJnios 
  (as 
  listed 
  

   by 
  Ortmann, 
  1912). 
  I 
  find 
  it 
  present 
  in 
  Pleurohema 
  sesajM 
  and 
  also 
  

   in 
  Unio 
  gihhosus, 
  for 
  which, 
  with 
  the 
  closely 
  related 
  forms, 
  Ortmann 
  

   has 
  created 
  the 
  new 
  genus 
  Elliptio. 
  

  

  Natural 
  infection. 
  — 
  When 
  the 
  investigation 
  of 
  the 
  breeding 
  of 
  this 
  

   mussel 
  was 
  undertaken 
  very 
  few 
  data 
  were 
  available; 
  in 
  fact, 
  the 
  

   published 
  accounts, 
  as 
  I 
  have 
  shown, 
  indicated 
  considerable 
  uncer- 
  

   tainty 
  about 
  the 
  breeding 
  period. 
  I 
  was 
  fortunate 
  in 
  finding 
  gravid 
  

   mussels 
  with 
  active 
  glochidia 
  in 
  considerable 
  abundance 
  and 
  suitable 
  

   for 
  experimentation. 
  Tiiis 
  situation 
  led 
  me 
  to 
  accept 
  the 
  opportunity 
  

   presented 
  before 
  I 
  was 
  able 
  to 
  mvestigate 
  sufficiently 
  the 
  problem 
  

   as 
  to 
  the 
  natural 
  host. 
  1 
  subjected 
  a 
  number 
  of 
  species 
  of 
  fish 
  to 
  

   infection, 
  obtaining 
  quite 
  definite 
  results. 
  The 
  following 
  species 
  

   carried 
  the 
  glochidia 
  successfull}" 
  on 
  the 
  gills 
  or 
  the 
  fins: 
  The 
  sunfish, 
  

   Lepomis 
  pallidus 
  (pi. 
  iv, 
  fig. 
  26&) 
  ; 
  the 
  catfishes, 
  Ictalurus 
  punctatus 
  

   and 
  Ameiurus 
  melas; 
  and 
  the 
  drum, 
  Aplodinotus 
  grunniens. 
  Some 
  

   months 
  after 
  these 
  experiments 
  were 
  made 
  Mr. 
  T. 
  Surber, 
  in 
  examina- 
  

   tion 
  of 
  Arkansas 
  fishes 
  taken 
  in 
  January, 
  reported 
  several 
  natural 
  

   infections 
  by 
  this 
  species 
  on 
  the 
  fins 
  of 
  a 
  sheepshead, 
  Aplodinotus 
  

   grunniens, 
  but 
  none 
  on 
  the 
  gills. 
  More 
  recently 
  I 
  have 
  had 
  the 
  

   opportunity 
  of 
  examining 
  a 
  number 
  of 
  fish 
  taken 
  in 
  the 
  Mississippi 
  

   at 
  three 
  different 
  stations. 
  Among 
  these 
  I 
  found 
  infected 
  by 
  the 
  

   larva 
  of 
  Q. 
  heros 
  five 
  species 
  of 
  fish 
  and 
  the 
  batrachian, 
  Necturus 
  

   maculosus. 
  These 
  observations 
  are 
  shown 
  in 
  detail 
  in 
  table 
  2. 
  

  

  The 
  infections 
  upon 
  Necturus 
  were 
  none 
  of 
  them 
  encysted, 
  even 
  

   after 
  attachment 
  for 
  a 
  known 
  period 
  of 
  several 
  days, 
  which 
  leads 
  me 
  

   to 
  believe 
  that 
  the 
  mussel 
  is 
  incapable 
  of 
  development 
  upon 
  this 
  host." 
  

  

  o 
  Incidentally 
  the 
  observation 
  may 
  be 
  of 
  interest 
  of 
  a 
  larval 
  mussel 
  of 
  another 
  species 
  abundant 
  upon 
  

   Necturus 
  completely 
  encysted 
  and 
  passing 
  through 
  its 
  metamorphosis 
  on 
  this 
  animal. 
  

  

  