﻿59 
  

  

  opod 
  niollusks 
  often 
  in 
  x>a*^«ing 
  into 
  the 
  adult 
  estate 
  

   cement 
  tlieir 
  larval 
  shell 
  to 
  the 
  feip 
  of 
  the 
  permanent 
  one, 
  

   it 
  oeeurred 
  to 
  me 
  that 
  these 
  little 
  cap-like 
  sti-uctures 
  on 
  

   the 
  tips 
  of 
  the 
  umbos 
  of 
  tlie 
  young 
  oysters, 
  must 
  in 
  like 
  

   manner 
  be 
  regarded 
  as 
  the 
  shell 
  of 
  the 
  oyster 
  larva 
  at 
  

   the 
  time 
  it 
  attaches 
  itself 
  to 
  a 
  foreign 
  objec^t. 
  Ux)on 
  

   comparing 
  the 
  outlines 
  of 
  the 
  supx^osed 
  larval 
  shells 
  of 
  

   our 
  oyster 
  with 
  those 
  shown 
  in 
  a 
  mounted 
  sx)ecinien 
  of 
  

   larval 
  oysters 
  taken 
  from 
  the 
  mantle 
  of 
  the 
  European 
  

   species, 
  I 
  found 
  the 
  likeness 
  very 
  striking 
  but 
  much 
  

   larger. 
  These 
  umbonal 
  affixed 
  larval 
  shells 
  measure 
  on 
  

   the 
  average 
  1-80 
  of 
  an 
  inch, 
  which 
  is 
  jDrobably 
  the 
  size 
  

   of 
  the 
  fry 
  at 
  the 
  time 
  of 
  fixation 
  and 
  are 
  rexn'esented 
  in 
  

   position 
  in 
  Fig. 
  viewed 
  from 
  within, 
  and 
  Fig. 
  7 
  from 
  

  

  Figures 
  6 
  and 
  7. 
  

  

  withouf. 
  Previous 
  to 
  attachment, 
  the 
  right 
  and 
  left 
  

   shells 
  of 
  both 
  the 
  American 
  and 
  the 
  Euroj^ean 
  s^^ecies 
  

   are 
  perfectly 
  symmetrical, 
  and 
  it 
  is 
  not 
  until 
  after 
  at- 
  

   tachment 
  takes 
  place 
  that 
  the 
  valves 
  show 
  a 
  disi^osition 
  

   to 
  become 
  unlike. 
  These 
  larval 
  shells 
  in 
  the 
  spat 
  I 
  

   have 
  examined 
  are 
  symmetrical, 
  which 
  is 
  almost 
  x)osi- 
  

   tive 
  proof 
  that 
  they 
  are 
  really 
  the 
  temporary 
  shelly 
  cov- 
  

   ering 
  of 
  the 
  fry 
  wlien 
  about 
  to 
  change 
  its 
  roving 
  habit 
  to 
  

  

  