﻿72 
  

  

  Fleinming 
  was 
  not 
  able 
  to 
  obtain 
  ranch 
  information 
  regard- 
  

   ing 
  the 
  history 
  of 
  the 
  digestive 
  tract, 
  but 
  as 
  he 
  has 
  conscien- 
  

   •ciously 
  adhered, 
  in 
  his 
  description, 
  (Eutwickelungsgeschichte 
  

   der 
  Najaden), 
  to 
  what 
  he 
  has 
  been 
  able 
  to 
  actually 
  see, 
  his 
  

   account 
  agrees 
  witli 
  Rabl's 
  so 
  far 
  as 
  it 
  goes, 
  and 
  there 
  is 
  every 
  

   reason 
  to 
  believe 
  that 
  the 
  process 
  is 
  the 
  same 
  in 
  Unio 
  and 
  

   Anodonta 
  and 
  the 
  oyster. 
  Flemming 
  shows 
  that 
  in 
  Anodon- 
  

   ta 
  the 
  single 
  large 
  macromere 
  divides 
  up 
  into 
  a 
  layer 
  of 
  large 
  

   cells 
  which 
  occupy 
  the 
  dorsal 
  surface 
  of 
  the 
  body, 
  and 
  subse- 
  

   quently 
  become 
  covered 
  by 
  the 
  shell, 
  but 
  he 
  was 
  not 
  able 
  to 
  

   trace 
  their 
  future 
  history. 
  

  

  The 
  various 
  accounts 
  of 
  the 
  origin 
  of 
  the 
  digestive 
  tract 
  in 
  

   the 
  Cycladidae 
  are 
  so 
  very 
  contradictory 
  and 
  irreconcilable 
  

   that 
  it 
  does 
  not 
  seem 
  worth 
  while 
  to 
  try 
  to 
  get 
  at 
  the 
  truth 
  

   by 
  comparing 
  them, 
  without 
  making 
  any 
  original 
  observations, 
  

   and 
  Kabl's 
  paper 
  and 
  my 
  own 
  fairly 
  represent 
  the 
  present 
  

   state 
  of 
  our 
  knowledge 
  of 
  the 
  origin 
  of 
  the 
  digestive 
  tract 
  in 
  

   Lamellibranchs. 
  The 
  difficulties 
  of 
  observation 
  are 
  so 
  great 
  

   that 
  the 
  observations 
  of 
  an 
  investigator 
  who 
  did 
  not 
  direct 
  

   especial 
  attention 
  to 
  the 
  subject 
  are 
  not 
  likely 
  to 
  afford 
  infor- 
  

   mation 
  of 
  much 
  value, 
  and 
  at 
  the 
  time 
  Loven's 
  paper 
  was 
  

   written 
  the 
  problems 
  of 
  invertebrate 
  embryology 
  were 
  so 
  dif- 
  

   ferent 
  from 
  those 
  of 
  the 
  present 
  day 
  that 
  no 
  conclusions 
  re- 
  

   garding 
  the 
  history 
  of 
  the 
  digestive 
  tract 
  can 
  be 
  drawn 
  from 
  

   his 
  figures. 
  

  

  THE 
  DEVELOPMENT 
  OF 
  THE 
  OYSTER 
  AND 
  THE 
  GASTRULA 
  THEORY. 
  

  

  Salensky 
  has 
  given 
  (Bemerkungen 
  iiber 
  Hseckel's 
  Gastraca 
  — 
  

   Theorie. 
  Arch. 
  f. 
  Naturgeschichte, 
  1874), 
  a 
  very 
  brief 
  ac- 
  

   count 
  of 
  the 
  origin 
  of 
  the 
  digestive 
  tract 
  in 
  the 
  oyster, 
  illus- 
  

   trated 
  by 
  three 
  figvires. 
  He 
  says, 
  p. 
  150, 
  " 
  das 
  erste 
  Stadium 
  

   der 
  Entwickelung 
  ein 
  Embryo 
  ist, 
  welcheraus 
  zwei 
  Schichten 
  

   besteht, 
  und 
  in 
  Inneren 
  keine 
  Ilohle 
  tragt," 
  Figure 
  1, 
  Taf. 
  

   V, 
  " 
  dass 
  sich 
  danu 
  verschiedene 
  aussere 
  Organe 
  und 
  eine 
  

   Mundeinstiilpung 
  bilden, 
  und 
  schliesslich 
  im 
  Inneren 
  des 
  En- 
  

   toderms 
  eine 
  Darmhohle 
  entsteht," 
  Figures 
  2 
  and 
  3. 
  

  

  After 
  a 
  very 
  exhaustive 
  and 
  able 
  review 
  of 
  the 
  facts 
  in 
  em- 
  

   bryology 
  with 
  which 
  we 
  were 
  at 
  that 
  time 
  acquainted, 
  he 
  con- 
  

  

  