﻿48 
  TEE 
  ZOOLOGIST. 
  

  

  Imperfect 
  pearls 
  are 
  formed 
  by 
  inserting 
  foreign 
  bodies 
  be- 
  

   tween 
  the 
  mantle 
  and 
  the 
  shell, 
  as 
  in 
  the 
  case 
  of 
  the 
  Chinese 
  

   forms 
  in 
  the 
  fresh-water 
  Dipsas 
  plicatus, 
  an 
  excellent 
  account 
  of 
  

   which 
  was 
  given 
  by 
  F. 
  Hague 
  in 
  1856.* 
  Circular 
  pearls 
  are 
  

   similarly 
  produced 
  round 
  silver 
  wire 
  or 
  other 
  substances, 
  and 
  

   Dr. 
  Eelaart 
  was 
  of 
  opinion 
  that 
  good 
  pearls 
  might 
  be 
  obtained 
  

   by 
  similar 
  treatment 
  of 
  the 
  Ceylonese 
  Pearl-Oyster, 
  but 
  such 
  has 
  

   yet 
  to 
  be 
  proved. 
  The 
  forthcoming 
  Report 
  of 
  Prof. 
  Herdman 
  

   will 
  probably 
  throw 
  light 
  on 
  this 
  and 
  other 
  interesting 
  points. 
  

   In 
  the 
  same 
  way 
  an 
  insect 
  in 
  a 
  fresh- 
  water 
  Mussel, 
  a 
  small 
  crab 
  

   and 
  a 
  fish 
  in 
  the 
  marine 
  Pearl-Oyster, 
  have 
  each 
  been 
  coated 
  

   with 
  the 
  nacreous 
  secretion. 
  

  

  A 
  recent 
  French 
  author, 
  M. 
  Leon 
  Diguet,t 
  attempts 
  to 
  draw 
  

   a 
  distinction 
  between 
  what 
  he 
  calls 
  nacreous 
  pearls 
  and 
  fine 
  

   pearls, 
  which, 
  he 
  affirms, 
  differ 
  from 
  each 
  other 
  in 
  form, 
  aspect, 
  

   constitution, 
  and 
  physiology. 
  He 
  holds 
  that 
  the 
  nacreous 
  pearl 
  

   is 
  a 
  concretion 
  of 
  the 
  mantle 
  poured 
  out 
  round 
  a 
  foreign 
  body, 
  as 
  

   in 
  the 
  case 
  of 
  the 
  Chinese 
  joss, 
  and 
  which 
  under 
  certain 
  circum- 
  

   stances 
  becomes 
  round. 
  It 
  is, 
  he 
  says, 
  a 
  product 
  of 
  the 
  surface 
  

   of 
  the 
  mantle. 
  

  

  The 
  fine 
  or 
  orient 
  pearl, 
  on 
  the 
  other 
  hand, 
  in 
  contrast 
  with 
  

   such 
  concretions, 
  is 
  found 
  in 
  the 
  interior 
  of 
  the 
  tissues 
  in 
  a 
  

   closed 
  chamber, 
  in 
  which 
  it 
  arrives 
  at 
  maturity. 
  During 
  its 
  

   evolution 
  it 
  passes 
  through 
  a 
  series 
  of 
  transformations, 
  of 
  which 
  

   he 
  gives 
  three 
  stages, 
  viz. 
  (1st) 
  its 
  appearance 
  in 
  a 
  liquid 
  state, 
  

   as 
  if 
  from 
  irritation 
  caused 
  by 
  a 
  parasite, 
  passing 
  (2nd) 
  in 
  virtue 
  

   of 
  the 
  elements 
  of 
  saturation 
  to 
  a 
  gelatinous 
  stage 
  like 
  conchy- 
  

   olin 
  ; 
  (3rd) 
  by 
  undergoing 
  progressive 
  calcification, 
  constituting 
  

   a 
  pearl 
  which 
  has 
  a 
  series 
  of 
  concentric 
  layers 
  caused 
  by 
  a 
  

   special 
  mechanism. 
  In 
  other 
  words, 
  the 
  concentric 
  stratification 
  

   is 
  affected 
  simultaneously 
  with 
  the 
  penetration 
  of 
  the 
  calcareous 
  

   solution 
  furnished 
  by 
  the 
  liquids 
  of 
  the 
  organism. 
  The 
  sac 
  or 
  

   pouch 
  is 
  subsequently 
  ruptured, 
  and 
  the 
  pearl 
  is 
  expelled. 
  

  

  While 
  this 
  ingenious 
  theory 
  does 
  credit 
  to 
  the 
  imagination 
  of 
  

   the 
  author, 
  it 
  unfortunately 
  is 
  at 
  variance 
  with 
  facts, 
  for, 
  so 
  far 
  

  

  ■■'■ 
  ' 
  Journ. 
  Roy. 
  Asiatic 
  Soc. 
  of 
  Great 
  Brit, 
  and 
  Ireland.' 
  Published 
  also 
  

   by 
  Von 
  Sicbold 
  in 
  ' 
  Zeit. 
  f. 
  w. 
  Zool.' 
  Bd. 
  viii. 
  pp. 
  139 
  154, 
  Taf. 
  xix. 
  and 
  xx. 
  

   | 
  ' 
  Bullet, 
  de 
  la 
  Soc. 
  Centrale 
  d'Agricult. 
  et 
  de 
  Peche,' 
  July, 
  lb'J9. 
  

  

  