﻿50 
  THE 
  ZOOLOGIST. 
  

  

  who, 
  by 
  a 
  hammer, 
  fix 
  in 
  wood 
  the 
  small 
  pearls 
  they 
  are 
  about 
  

   to 
  drill 
  ; 
  and 
  Dr. 
  George 
  Harley's 
  experience 
  was 
  similar. 
  

   Dealers 
  also 
  use 
  their 
  teeth 
  to 
  distinguish 
  between 
  real 
  and 
  

   fictitious 
  pearls. 
  

  

  In 
  the 
  analyses 
  of 
  pearls 
  made 
  in 
  1888 
  by 
  Dr. 
  George 
  

   Harley,* 
  it 
  was 
  found 
  that 
  British, 
  Australian, 
  and 
  Ceylonese 
  

   pearls 
  all 
  agreed 
  in 
  consisting 
  only 
  of 
  calcium 
  carbonate, 
  organic 
  

   matter, 
  and 
  water. 
  There 
  was 
  a 
  total 
  absence 
  of 
  magnesia, 
  and 
  

   of 
  all 
  the 
  other 
  mineral 
  ingredients 
  of 
  sea-water. 
  No 
  phosphates 
  

   occurred 
  in 
  them 
  (though 
  Eudler 
  says 
  they 
  are 
  present 
  (Encyclop. 
  

   Brit.)). 
  His 
  (Eudler's) 
  analysis 
  was 
  91'72 
  per 
  cent, 
  of 
  carbonate 
  

   of 
  lime, 
  5'94 
  of 
  organic 
  matter, 
  2*23 
  of 
  water, 
  and 
  O'll 
  loss 
  ; 
  

   and 
  he 
  observes 
  that 
  mother-of-pearl 
  (that 
  is, 
  the 
  nacreous 
  layer 
  

   of 
  the 
  shell) 
  contained 
  less 
  than 
  half 
  the 
  quantity 
  of 
  organic 
  

   matter 
  the 
  pearl 
  did. 
  

  

  Age 
  of 
  Pearl-bearing 
  Sliclls.—Few 
  pearls 
  occur 
  before 
  the 
  

   third 
  year 
  in 
  the 
  marine 
  Pearl-Oysters; 
  indeed, 
  it 
  is 
  considered 
  

   that 
  shells 
  which 
  are 
  five 
  years 
  old 
  offer 
  the 
  best 
  field 
  for 
  pearls. 
  

   From 
  the 
  fifth 
  to 
  the 
  sixth 
  year 
  the 
  Pearl-Oyster 
  becomes 
  more 
  

   valuable, 
  especially 
  so 
  in 
  the 
  seventh 
  year 
  ; 
  the 
  Japanese, 
  

   indeed, 
  have 
  them 
  up 
  to 
  the 
  ninth 
  year. 
  In 
  the 
  fresh-water 
  

   forms, 
  such 
  as 
  the 
  Mussel 
  of 
  the 
  Tay, 
  pearls 
  occur 
  in 
  small 
  

   shells, 
  but 
  it 
  does 
  not 
  follow 
  that 
  the 
  shell 
  is 
  very 
  young. 
  The 
  

   Americans 
  consider 
  from 
  three 
  to 
  five 
  years 
  as 
  the 
  fruitful 
  period 
  

   for 
  pearls 
  in 
  their 
  fresh 
  -water 
  Mussels, 
  t 
  

  

  Frequency 
  of 
  Occurrence 
  of 
  Pearls. 
  — 
  The 
  frequency 
  of 
  the 
  

   occurrence 
  of 
  pearls 
  in 
  the 
  various 
  marine 
  and 
  fresh-water 
  

   shells 
  is 
  fixed 
  by 
  no 
  law. 
  Hundreds 
  of 
  pearl-shells 
  may 
  be 
  

   examined 
  without 
  finding 
  a 
  single 
  pearl 
  ; 
  but, 
  on 
  the 
  other 
  hand, 
  

   a 
  single 
  Ceylonese 
  shell 
  will 
  occasionally 
  produce 
  a 
  pearl 
  worth 
  

   a 
  thousand 
  pounds. 
  An 
  experienced 
  pearl-fisherman 
  of 
  the 
  

   Tay 
  considered 
  that 
  perhaps 
  one 
  in 
  a 
  hundred 
  contained 
  a 
  

   pearl. 
  In 
  a 
  group 
  of 
  thirty-one 
  examined 
  by 
  Mr. 
  Alex. 
  J. 
  H. 
  

   Kussell, 
  M.A., 
  fifteen 
  had 
  no 
  pearls, 
  and 
  sixteen 
  had 
  one 
  or 
  

   more 
  ; 
  so 
  that 
  nearly 
  50 
  per 
  cent, 
  in 
  this 
  instance 
  had 
  pearls 
  of 
  

   a 
  kind, 
  for 
  they 
  were 
  of 
  no 
  value. 
  Of 
  these 
  eight 
  contained 
  

  

  * 
  ' 
  Proceed. 
  R. 
  S.' 
  vol. 
  xlviii. 
  p. 
  402. 
  

  

  f 
  Prof. 
  Herdinan 
  thinks 
  there 
  is 
  little 
  or 
  no 
  superficial 
  increase 
  of 
  the 
  

   shells 
  after 
  the 
  fourth 
  year, 
  though 
  they 
  may 
  grow 
  thicker. 
  Op. 
  cit., 
  p. 
  136. 
  

  

  