﻿[3] 
  PEARLS 
  AT 
  TAHITI 
  AND 
  TUAMOTU. 
  355 
  

  

  Origin 
  of 
  pearls. 
  — 
  The 
  finest 
  and 
  most 
  valuable 
  pearls 
  owe 
  their 
  origin 
  

   to 
  a 
  small 
  and 
  very 
  modest 
  little 
  shellfish, 
  occupying 
  a 
  very 
  low 
  grade 
  

   in 
  the 
  animal 
  kingdom, 
  the 
  pearl-oyster 
  (Meleagrina 
  margaritifera, 
  and 
  

   a 
  smaller 
  variety, 
  Meleagrina 
  radiata). 
  Beds 
  of 
  pearls, 
  properly 
  speak- 
  

   ing, 
  do 
  not 
  exist. 
  There 
  are 
  beds 
  of 
  shell 
  -fish 
  producing 
  pearls, 
  but 
  

   pearls 
  are 
  not 
  found 
  on 
  the 
  sands 
  of 
  the 
  sea, 
  except 
  in 
  rare 
  and 
  accidental 
  

   cases. 
  

  

  Fine 
  pearls 
  are 
  not 
  produced 
  exclusively 
  by 
  the 
  pearl-oyster; 
  but 
  they 
  

   are 
  also 
  found 
  in 
  the 
  shell 
  -fish, 
  commonly 
  called 
  "hog 
  mussel"; 
  in 
  the 
  

   "mulctte 
  margaritifere," 
  common 
  in 
  fresh 
  water, 
  the 
  valves 
  of 
  which 
  are 
  

   used 
  by 
  gilders 
  in 
  preparing 
  their 
  gilding; 
  in 
  the 
  " 
  benitiersf 
  a 
  shell 
  

   belonging 
  to 
  the 
  conchiferous 
  Acephala, 
  in 
  the 
  Haliotidce, 
  &c. 
  In 
  the 
  

   pearl-oyster, 
  however, 
  the 
  finest 
  and 
  most 
  highly 
  valued 
  pearls 
  are 
  gen- 
  

   erally 
  found. 
  

  

  Formation 
  of 
  pearls. 
  — 
  The 
  question 
  as 
  to 
  what 
  is 
  the 
  cause 
  of 
  the 
  for. 
  

   matiou 
  of 
  pearls 
  has 
  frequently 
  been 
  discussed, 
  and 
  has 
  been 
  studied 
  to 
  

   some 
  extent, 
  but 
  it 
  has 
  not 
  yet 
  been 
  satisfactorily 
  answered. 
  The 
  best 
  

   work 
  on 
  the 
  subject 
  is 
  that 
  published 
  by 
  Mobius 
  in 
  1858. 
  Since 
  then 
  

   nothing 
  has 
  been 
  said 
  which 
  is 
  not 
  already 
  found 
  in 
  the 
  work 
  of 
  this 
  

   naturalist. 
  Mobius 
  does 
  not 
  solve 
  the 
  problem 
  of 
  the 
  first 
  origin. 
  He 
  

   says 
  that 
  the 
  kernel 
  or 
  nucleus 
  around 
  which 
  the 
  pearl 
  forms 
  is 
  formed 
  

   by 
  bodies 
  foreign 
  to 
  the 
  oyster; 
  such 
  as 
  calcareous 
  crystals, 
  entozoa, 
  

   auodonta, 
  distoma, 
  sometimes 
  an 
  Ggg 
  lodged 
  in 
  a 
  corner 
  of 
  the 
  genital 
  

   gland, 
  organic, 
  amorphous, 
  brown, 
  or 
  yellowish 
  debris, 
  &c. 
  But 
  how 
  

   these 
  bodies 
  found 
  their 
  way 
  into 
  the 
  tissues 
  where 
  the 
  pearl 
  originates 
  

   no 
  investigation 
  has 
  as 
  yet 
  settled. 
  

  

  The 
  further 
  development 
  of 
  the 
  pearl, 
  and 
  its 
  structure, 
  are 
  better 
  

   known. 
  The 
  pearl 
  is 
  formed 
  like 
  the 
  mother-of-pearl 
  layer 
  of 
  a 
  scale. 
  

   It 
  is 
  the 
  product 
  of 
  a 
  secretion 
  of 
  the 
  tissues 
  of 
  the 
  oyster 
  round 
  a 
  

   nucleus 
  ; 
  in 
  other 
  words, 
  it 
  is 
  a 
  shell 
  reversed. 
  In 
  the 
  center 
  is 
  the 
  

   nucleus 
  around 
  which 
  there 
  is 
  an 
  epidermic 
  layer; 
  over 
  this 
  a 
  layer 
  of 
  

   prisms 
  (calcareous 
  prisms 
  with 
  six 
  sides, 
  like 
  the 
  prisms 
  of 
  the 
  enamel 
  

   of 
  the 
  teeth), 
  and 
  finally 
  a 
  third 
  layer, 
  called 
  by 
  Mobius, 
  the 
  mother-of- 
  

   pearl 
  layer, 
  to 
  which 
  are 
  added 
  several 
  concentric 
  layers 
  secreted 
  by 
  

   the 
  tissues, 
  and 
  which 
  produce 
  the 
  continuous 
  growth 
  of 
  the 
  mother-of- 
  

   pearl 
  layer. 
  As 
  in 
  the 
  teeth, 
  the 
  structure 
  of 
  the 
  pearl 
  comprises 
  an 
  

   organic 
  azotic 
  cover 
  and 
  hard 
  parts, 
  the 
  latter 
  soluble 
  in 
  acids. 
  The 
  

   coloring 
  and 
  reflection 
  is 
  due 
  to 
  metallic 
  salts. 
  

  

  Pearls 
  may 
  be 
  found 
  in 
  nearly 
  all 
  parts 
  of 
  the 
  oyster 
  — 
  in 
  the 
  genital 
  

   gland, 
  in 
  and 
  around 
  the 
  adductor 
  muscle, 
  and 
  in 
  the 
  mantle. 
  There 
  

   may 
  be 
  fixed 
  ones 
  on 
  the 
  shell, 
  or 
  some, 
  covered 
  up 
  by 
  growth 
  but 
  

   originally 
  external, 
  in 
  the 
  shell 
  itself. 
  The 
  pearls 
  found 
  on 
  the 
  body 
  of 
  

   the 
  mollusk 
  are 
  considered 
  the 
  finest 
  and 
  purest. 
  Their 
  form 
  approaches 
  

   that 
  of 
  a 
  perfect 
  sphere. 
  These 
  are 
  the 
  ones 
  which 
  are 
  called 
  " 
  virgin 
  " 
  

   or 
  "paragon" 
  pearls. 
  They 
  are 
  nearly 
  always 
  found 
  in 
  the 
  periphery 
  

   pf 
  the 
  gland 
  and 
  in 
  the 
  lower 
  portion 
  of 
  the 
  same. 
  Held 
  merely 
  by 
  the 
  

  

  