﻿8 
  

  

  posited 
  as 
  they 
  are 
  internally, 
  as 
  growth 
  proceeds 
  pro- 
  

   jeet 
  in 
  succession 
  past 
  each 
  other 
  at 
  the 
  free 
  edges 
  of 
  the 
  

   valves 
  and 
  external 
  surface 
  of 
  the 
  shell, 
  so 
  that 
  the 
  suc- 
  

   cessive 
  deposits 
  may 
  frequently 
  he 
  distinguished, 
  espe- 
  

   pecially, 
  as 
  these 
  deposits 
  seem 
  to 
  be 
  laid 
  down 
  periodi- 
  

   cally, 
  giving 
  rise 
  to 
  a 
  very 
  rough 
  iml)ricated 
  appearance 
  

   of 
  the 
  edges 
  of 
  the 
  hiyers 
  on 
  the 
  outside 
  of 
  the 
  shell. 
  

   The 
  inner 
  pearly 
  or 
  nacreous 
  layers 
  of 
  the 
  shell 
  are 
  dif- 
  

   ferent 
  in 
  structure 
  from 
  the 
  outer 
  ones. 
  These 
  are 
  made 
  

   up 
  of 
  microscopic 
  prisms 
  of 
  carbonate 
  of 
  lime 
  embedded 
  

   in 
  a 
  matrix 
  of 
  horny 
  substance, 
  analogous, 
  if 
  not 
  identi- 
  

   cal 
  with 
  tlie 
  substance 
  whicli 
  forms 
  the 
  external 
  hard 
  

   parts 
  of 
  insects 
  The 
  outer 
  po]-ti(»n 
  of 
  the 
  shell, 
  forming 
  

   much 
  the 
  largest 
  proportion 
  of 
  the 
  whole, 
  is 
  differently 
  

   constituted 
  according 
  to 
  Nathusius-Konigsborn'", 
  who 
  

   •finds 
  that 
  in 
  the 
  shells 
  of 
  the 
  oyster 
  of 
  Europe 
  there 
  are 
  

   superimposed 
  cavities, 
  tilled 
  in 
  life 
  with 
  water, 
  which 
  

   lie 
  just 
  beneath 
  the 
  inner 
  pearly 
  layers 
  and 
  between 
  the 
  

   attachment 
  of 
  the 
  muscle 
  and 
  the 
  hinge 
  corresponding 
  

   to 
  the 
  thickened 
  nacreous 
  portion. 
  In 
  the 
  thick 
  margi- 
  

   nal 
  portion 
  of 
  the 
  shell, 
  extending 
  from 
  a 
  point 
  half 
  way 
  

   l)etween 
  the 
  insertion 
  of 
  the 
  muscle 
  and 
  hinge, 
  to 
  near 
  

   the 
  edge 
  of 
  the 
  valves, 
  he 
  finds 
  still 
  another 
  series 
  of 
  

   closed 
  cavities 
  which 
  are 
  separated 
  by 
  oblique 
  divisions 
  

   of 
  a 
  laminar 
  character, 
  and 
  which 
  ;ire 
  tilled 
  with 
  a 
  singu- 
  

   lar 
  structure 
  of 
  minute 
  cavities 
  which 
  contain 
  air. 
  The 
  

   hrst 
  kind 
  or 
  the 
  water 
  bearing 
  cavities 
  are, 
  it 
  may 
  be 
  

   well 
  to 
  remark, 
  greatly 
  develoj^^^d 
  in 
  t<potidy]ns\ 
  an 
  ally 
  

   of 
  the 
  oyster. 
  The 
  laminar 
  character 
  of 
  the 
  shell 
  is 
  

   apparent 
  from 
  the 
  presence 
  of 
  \ery 
  line 
  lines 
  of 
  growth 
  

   even 
  on 
  the 
  valves 
  of 
  the 
  fiee-swimmiug 
  embryos, 
  and 
  

   in 
  the 
  embryonic 
  shell 
  which 
  covers 
  like 
  a 
  little 
  raised 
  

   cap 
  the 
  extreme 
  tips 
  of 
  the 
  umbos 
  or 
  hinge 
  ends 
  of 
  the 
  

   valves 
  of 
  attached 
  spat 
  i 
  to 
  1 
  inch 
  in 
  diameter. 
  

  

  During 
  the 
  past 
  season 
  I 
  endeavored 
  to 
  ascertain 
  if 
  it 
  

  

  *Vintersuchungi;n 
  ueber 
  nicht 
  cellul 
  re 
  Organismen, 
  namentlich 
  ; 
  Crustaceen-panzer, 
  Mol- 
  

   lusken— 
  Sr.halen 
  unci 
  P^ihiillen. 
  Von 
  W. 
  Von 
  Nathusius-Ki'.nigsborn. 
  4 
  to., 
  pp. 
  144, 
  pis. 
  16. 
  

  

  Berlin, 
  1877. 
  

  

  