﻿PEOPAGATION 
  OF 
  FRESH-WATER 
  MUSSELS. 
  35 
  

  

  GENERAL 
  DISCUSSION. 
  

  

  In 
  the 
  investigation 
  of 
  the 
  specific 
  problem 
  of 
  propagating 
  the 
  

   Quadrulas 
  some 
  results 
  have 
  been 
  attained 
  which 
  are 
  of 
  general 
  

   application 
  probably 
  to 
  all 
  the 
  Unionidse. 
  Also 
  observations 
  have 
  

   been 
  made 
  ijicidentally 
  upon 
  other 
  species 
  which, 
  as 
  they 
  have 
  a 
  

   bearing 
  on 
  the 
  present 
  problem, 
  require 
  discussion. 
  

  

  REPRODUCTION 
  AND 
  EMBRYONIC 
  STAGES. 
  

  

  As 
  practical 
  propagation 
  of 
  the 
  Unionidse 
  is 
  only 
  indirectly 
  con- 
  

   cerned 
  with 
  the 
  embryonic 
  stages, 
  I 
  have 
  not 
  dealt 
  with 
  these 
  in 
  the 
  

   body 
  of 
  this 
  paper. 
  My 
  observations 
  upon 
  these 
  stages 
  have 
  been 
  

   very 
  limited 
  and 
  incidental 
  only 
  to 
  other 
  studies, 
  but 
  as 
  the 
  Quadrulas 
  

   have 
  had 
  little 
  attention 
  some 
  of 
  these 
  may 
  be 
  worth 
  mentioning. 
  

   Reproduction 
  among 
  the 
  Quadrulas 
  seems 
  to 
  be 
  essentially 
  as 
  reported 
  

   in 
  other 
  Unionidae 
  (Rabl, 
  1876; 
  Schierholz, 
  1888; 
  Latter, 
  1891: 
  

   LilUe, 
  1895). 
  The 
  sexes 
  are 
  separate 
  so 
  far 
  as 
  known. 
  The 
  gonads 
  

   occupy 
  a 
  considerable 
  portion 
  of 
  the 
  visceral 
  mass 
  among 
  the 
  coils 
  

   of 
  the 
  Intestine. 
  The 
  eggs 
  upon 
  extrusion 
  from 
  the 
  genital 
  apertures 
  

   pass 
  into 
  the 
  suprabranchial 
  chambers 
  of 
  the 
  Inner 
  giUs, 
  passing 
  from 
  

   there 
  to 
  the 
  cloaca 
  and 
  then 
  back 
  through 
  the 
  suprabranchial 
  cham- 
  

   bers 
  to 
  the 
  giUs. 
  They 
  are 
  probably 
  fertilized 
  during 
  transition 
  to 
  

   the 
  gills 
  by 
  sperms 
  introduced 
  with 
  the 
  respiratory 
  current. 
  I 
  have 
  

   observed 
  ovulation 
  in 
  Quadrula 
  ebena 
  and 
  remarked 
  the 
  exceedingly 
  

   fine 
  stream 
  of 
  eggs 
  issuing 
  singly 
  and 
  covered 
  by 
  mucous 
  envelope; 
  

   the 
  passage 
  to 
  the 
  gills 
  was 
  not 
  observed, 
  but 
  it 
  would 
  seem 
  strange 
  

   in 
  these 
  forms 
  wliich 
  carry 
  embryos 
  in 
  all 
  four 
  gills 
  that 
  the 
  eggs 
  

   should 
  not 
  go 
  directly 
  mto 
  the 
  inner 
  gills, 
  as 
  they 
  must 
  pass 
  the 
  

   openings 
  of 
  the 
  water 
  tubes. 
  

  

  Contributions 
  to 
  a 
  knowledge 
  of 
  the 
  development 
  from 
  the 
  eggs 
  to 
  

   the 
  glochidial 
  stage 
  among 
  Unionidse 
  have 
  been 
  made 
  by 
  Flemming 
  

   (1875), 
  Schierholz 
  (1878, 
  1888), 
  Goette 
  (1891), 
  and 
  these 
  stages 
  have 
  

   been 
  completely 
  described 
  for 
  Vnio 
  complanata 
  and 
  Anodonta 
  cataracta 
  

   by 
  Lillie 
  (1895). 
  

  

  While 
  making 
  examinations 
  for 
  breeding 
  periods 
  I 
  was 
  much 
  

   astonished 
  to 
  note 
  the 
  slowness 
  of 
  division 
  processes. 
  The 
  eggs 
  of 
  

   Q. 
  ebena 
  examined 
  in 
  the 
  morning 
  of 
  May 
  31 
  seemed 
  to 
  be 
  all 
  in 
  the 
  

   one-celled 
  stage; 
  in 
  the 
  afternoon 
  two-celled 
  stages 
  were 
  present. 
  

   The 
  second 
  day 
  segmentation 
  had 
  advanced 
  to 
  the 
  four- 
  and 
  eight- 
  

   celled 
  stages 
  only, 
  and 
  the 
  fourth 
  day 
  16-ceDed 
  stages 
  predominated. 
  

   Since 
  making 
  these 
  observations 
  I 
  have 
  read 
  Lilhe's 
  (1895) 
  paper 
  

   and 
  see 
  that 
  he 
  has 
  commented 
  upon 
  the 
  phenomenally 
  slow 
  seg- 
  

   mentation 
  in 
  the 
  forms 
  which 
  he 
  examined, 
  Vnio 
  coinplanata 
  and 
  

   Anodonta 
  cataracta, 
  contrasting 
  it 
  with 
  the 
  rapid 
  development 
  in 
  

   marine 
  lameUibranchs. 
  

  

  