﻿54: 
  

  

  jnent 
  of 
  Unio 
  (Entwickelungsgeschichte 
  der 
  Malermiiscliel, 
  

   Figures 
  28 
  to 
  32), 
  which 
  is 
  very 
  similar 
  to 
  this, 
  both 
  in 
  out- 
  

   line 
  and 
  in 
  internal 
  structure, 
  and 
  Fleniming 
  has 
  figured 
  a 
  

   very 
  similar 
  stage 
  in 
  Anodonta 
  (Entwickelungsgeschichte 
  der 
  

   Najaden, 
  Taf. 
  II 
  Figure 
  32), 
  but 
  each 
  of 
  these 
  authors 
  re- 
  

   gards 
  the 
  surface 
  where 
  the 
  polar 
  globule 
  is 
  placed 
  as 
  poste- 
  

   rior. 
  The 
  published 
  acconnts 
  of 
  the 
  transformation 
  of 
  the 
  

   glochidium 
  into 
  the 
  adult 
  Unio 
  or 
  Anodonta 
  (Ueber 
  die 
  post- 
  

   embryonale 
  Entwickelung 
  iinserer 
  Siisswassermnscheln 
  (Ano- 
  

   donta), 
  von 
  Dr. 
  M. 
  Braun 
  in 
  Wiirzbui'g. 
  and: 
  Zur 
  Entwicke- 
  

   lungsgeschichte 
  der 
  Teich- 
  und 
  Flussmuschel. 
  von 
  Carl 
  

   Schierholz.) 
  are 
  not 
  sufficiently 
  explicit 
  to 
  decide 
  what 
  the 
  

   relation 
  between 
  the 
  body 
  of 
  the 
  larva 
  and 
  that 
  of 
  the 
  adult 
  

   really 
  is, 
  and 
  until 
  some 
  one 
  publishes 
  a 
  satisfactory 
  illus- 
  

   trated 
  account 
  of 
  the 
  transformation, 
  the 
  fact 
  that 
  the 
  velum 
  

   of 
  the 
  oyster 
  certainly 
  makes 
  its 
  appearance 
  at 
  the 
  point 
  

   which 
  is 
  occupied 
  by 
  the 
  polar 
  globule 
  must 
  lead 
  us 
  to 
  believe 
  

   that 
  Flemming 
  and 
  Rabl 
  are 
  in 
  error, 
  and 
  that 
  the 
  region 
  

   between 
  the 
  letters 
  a 
  and 
  i 
  of 
  Eabl's 
  l^igure 
  28, 
  is 
  that 
  

   which 
  is 
  occupied 
  by 
  the 
  velum 
  in 
  the 
  the 
  marine 
  Lamelli- 
  

   branchs, 
  and 
  therefore 
  the 
  anterior. 
  

  

  The 
  free-swimming 
  stage 
  may 
  be 
  reached, 
  under 
  excep- 
  

   tionally 
  favorable 
  circumstances, 
  within 
  two 
  hours 
  after 
  im- 
  

   pregnation, 
  but 
  it 
  is 
  not 
  usual 
  for 
  the 
  embryo 
  to 
  attain 
  to 
  this 
  

   degree 
  of 
  development 
  in 
  less 
  than 
  twenty-ibur 
  hours, 
  and 
  it 
  

   may 
  require 
  more 
  than 
  two 
  days 
  to 
  reach 
  it. 
  The 
  duration 
  

   of 
  this 
  stage 
  also 
  varies 
  greatly, 
  but 
  after 
  from 
  one 
  to 
  twelve 
  

   hours 
  the 
  embryo 
  will 
  be 
  found 
  to 
  have 
  assumed 
  the 
  form 
  

   shown 
  in 
  Figure 
  30, 
  which 
  is 
  the 
  same 
  view 
  as 
  Figure 
  32. 
  

   The 
  outline 
  of 
  the 
  body 
  has 
  not 
  undergone 
  much 
  change, 
  and 
  

   the 
  anterior 
  end 
  is 
  still 
  rounded 
  and 
  carries 
  the 
  velum, 
  while 
  

   the 
  pointed 
  anal 
  papilla, 
  «, 
  occupies 
  the 
  posterior 
  end. 
  The 
  

   foot-like 
  protuberance 
  on 
  the 
  ventral 
  surface 
  has 
  disappeared, 
  

   and 
  the 
  blastopore 
  on 
  the 
  dorsal 
  surface 
  has 
  entirely 
  closed, 
  and 
  

   the 
  ectoderm 
  has 
  become 
  continuous 
  over 
  it, 
  thus 
  leaving 
  the 
  

   ended 
  erm 
  as 
  a 
  sphei'ical 
  body 
  of 
  cells 
  inside 
  the 
  body 
  cavity. 
  

   I 
  was 
  not 
  able 
  to 
  discover 
  any 
  central 
  cavity 
  inside 
  this 
  mass, 
  

   but 
  the 
  cells 
  are 
  so 
  opaque 
  that 
  it 
  would 
  be 
  very 
  difficult 
  to 
  

  

  