﻿56 
  THE 
  ZOOLOGIST. 
  

  

  out 
  that 
  M. 
  G. 
  Seurat 
  has 
  just 
  found 
  a 
  cestode 
  parasite 
  as 
  the 
  

   cause 
  of 
  pearl-forination 
  in 
  the 
  region 
  of 
  the 
  Gambia. 
  An 
  older 
  

   stage, 
  moreover, 
  occurred 
  in 
  Batistes. 
  

  

  It 
  is 
  interesting 
  also 
  to 
  observe 
  that 
  the 
  behaviour 
  of 
  the 
  

   Pearl-Oyster 
  spat* 
  is 
  in 
  most 
  respects 
  the 
  same 
  as 
  that 
  of 
  young 
  

   Mussels, 
  even 
  to 
  the 
  coating 
  of 
  seaweeds 
  and 
  zoophytes, 
  and 
  

   their 
  habit 
  of 
  detaching 
  themselves 
  at 
  will. 
  

  

  For 
  the 
  photographs 
  of 
  sections 
  of 
  pearls, 
  I 
  have 
  to 
  thank 
  

   my 
  colleague, 
  Prof. 
  Musgrove, 
  who 
  kindly 
  undertook 
  the 
  work. 
  

   Figs. 
  2, 
  3, 
  4, 
  and 
  5 
  were 
  printed 
  by 
  Mr. 
  A. 
  W. 
  Brown, 
  of 
  the 
  

   Gatty 
  Marine 
  Laboratory. 
  

  

  Plate 
  I. 
  

  

  Fig. 
  1. 
  — 
  Section 
  of 
  a 
  Tay 
  pearl 
  iu 
  its 
  natural 
  condition. 
  The 
  

   radiating 
  and 
  concentric 
  lines 
  are 
  boldly 
  indicated. 
  This 
  specimen 
  was 
  

   presented 
  by 
  B. 
  C. 
  Cox, 
  Esq., 
  of 
  St. 
  Andrews. 
  Magnified. 
  

  

  Fig. 
  2. 
  — 
  Section 
  of 
  a 
  Tay 
  pearl 
  after 
  decalcification. 
  The 
  whole 
  

   field 
  is 
  minutely 
  reticulated, 
  and 
  traces 
  of 
  two 
  nuclei 
  are 
  indicated. 
  

   Magnified. 
  

  

  Fig. 
  3. 
  — 
  Section 
  of 
  a 
  decalcified 
  pearl 
  from 
  the 
  Pearl-Mussel 
  of 
  

   the 
  Tay, 
  made 
  like 
  the 
  former 
  by 
  Mr. 
  A. 
  J. 
  H. 
  Russell, 
  M.A. 
  The 
  

   radiating 
  lines 
  of 
  conchyolin 
  are 
  very 
  prominent, 
  whereas 
  the 
  con- 
  

   centric 
  lines 
  are 
  less 
  so. 
  Magnified. 
  

  

  Fig. 
  4. 
  — 
  Section 
  of 
  a 
  decalcified 
  pearl 
  in 
  its 
  capsule 
  from 
  the 
  

   mautle 
  of 
  the 
  Common 
  Mussel. 
  In 
  this 
  the 
  conchyolin 
  forms 
  fine 
  

   concentric 
  striae 
  around 
  the 
  nucleus. 
  No 
  radiating 
  lines 
  are 
  visible. 
  

   The 
  ova 
  of 
  the 
  Mussel 
  (a 
  female) 
  fill 
  up 
  the 
  mantle 
  beyond 
  the 
  capsule 
  

   of 
  the 
  pearl. 
  Magnified. 
  

  

  Fig. 
  5. 
  — 
  Section 
  of 
  a 
  decalcified 
  pearl 
  (small) 
  in 
  the 
  mantle 
  of 
  a 
  

   Pearl-Mussel 
  from 
  the 
  Tay.f 
  It 
  is 
  surrounded 
  by 
  a 
  well-formed 
  cellular 
  

   capsule. 
  Minute 
  reticulations 
  and 
  concentric 
  lines 
  of 
  growth 
  are 
  

   visible, 
  as 
  well 
  as 
  several 
  nuclei. 
  Magnified. 
  

  

  * 
  ' 
  Nature,' 
  Dec. 
  10th, 
  1903, 
  p. 
  69. 
  

  

  f 
  I 
  have 
  to 
  thank 
  Mr. 
  Lurusden, 
  the 
  Superintendent 
  of 
  the 
  Tay 
  Salmon 
  

   Fisheries, 
  for 
  bis 
  courtesy 
  in 
  forwarding 
  living 
  examples 
  of 
  the 
  Pearl- 
  

   Mussels. 
  

  

  