﻿380 
  JOHN 
  RENNIE. 
  

  

  groups, 
  it 
  appears 
  that 
  very 
  little 
  has 
  been 
  clone 
  in 
  tlie 
  

   investigation 
  of 
  the 
  lower 
  vertebrates. 
  Indeed, 
  until 
  a 
  short 
  

   time 
  ago, 
  tliere 
  appears 
  to 
  have 
  been 
  some 
  doubt 
  as 
  to 
  their 
  

   existence 
  in 
  cold-blooded 
  animals. 
  According 
  to 
  Laguesse 
  

   (7), 
  " 
  Les 
  ilots 
  de 
  Langerhans 
  paraissent 
  constants 
  chez 
  les 
  

   Mammiferes 
  et 
  les 
  Oiseaux, 
  leur 
  existence 
  est 
  douteuse 
  chez 
  

   les 
  Vertebres 
  inf 
  erieurs. 
  . 
  . 
  . 
  Les 
  auteurs 
  ne 
  les 
  signalent 
  pas 
  

   en 
  general 
  chez 
  les 
  Vertebres 
  inferieurs; 
  Lewaschew 
  les 
  a 
  

   cherches 
  et 
  ne 
  les 
  a 
  jamais 
  trouves 
  chez 
  les 
  animaux 
  a 
  sang 
  

   froid; 
  Harris 
  and 
  Gow 
  ne 
  les 
  ont 
  pas 
  vus 
  chez 
  les 
  Eeptiles, 
  

   mais 
  pretendent 
  les 
  apercevoir 
  chez 
  la 
  grenouille 
  ; 
  Von 
  Ebner 
  

   les 
  y 
  a 
  decrits 
  egalement. 
  Enfin, 
  quelques 
  points 
  des 
  descrip- 
  

   tions 
  d'Ogata 
  et 
  de 
  Platner 
  pourraient 
  s'iuterpreter 
  en 
  favour 
  

   de 
  leur 
  existence." 
  No 
  reference 
  is 
  made 
  to 
  their 
  possible 
  

   occurrence 
  in 
  fishes. 
  Indeed, 
  Harris 
  and 
  Gow, 
  whom 
  

   Laguesse 
  quotes, 
  expressly 
  state 
  that 
  in 
  consequence 
  of 
  their 
  

   doubt 
  as 
  to 
  the 
  nature 
  of 
  the 
  so-called 
  pancreas 
  in 
  fishes 
  

   they 
  did 
  not 
  investigate 
  the 
  group. 
  In 
  the 
  following 
  year, 
  

   however, 
  Laguesse 
  recorded 
  the 
  existence 
  of 
  cell-islets 
  in 
  the 
  

   pancreas 
  of 
  Crenilabrus 
  ; 
  in 
  1898, 
  Massari 
  (12) 
  described 
  

   them 
  in 
  the 
  eel 
  (An 
  gu 
  ill 
  a 
  vulgaris); 
  and 
  in 
  1899 
  Dlamare 
  

   (3), 
  in 
  an 
  important 
  paper, 
  established 
  their 
  occurrence 
  in 
  six 
  

   different 
  species 
  of 
  Teleostei, 
  as 
  well 
  as 
  in 
  all 
  the 
  other 
  verte- 
  

   brate 
  divisions. 
  I 
  shall 
  have 
  occasion 
  later 
  on 
  to 
  refer 
  to 
  the 
  

   work 
  and 
  opinions 
  of 
  these 
  writers. 
  

  

  In 
  the 
  investigation 
  of 
  which 
  tlie 
  present 
  paper 
  is 
  a 
  partial 
  

   account 
  attention 
  has 
  been 
  limited 
  to 
  the 
  bony 
  fishes, 
  of 
  which 
  

   about 
  twenty-five 
  different 
  species 
  have 
  been 
  studied. 
  In 
  

   general 
  these 
  islets 
  are 
  fewer 
  in 
  number 
  and 
  proportionately 
  

   larger 
  than 
  in 
  mammals. 
  Owing 
  to 
  the 
  diffuse 
  condition 
  of 
  the 
  

   pancreas 
  in 
  most 
  Teleostei, 
  they 
  may, 
  even 
  when 
  minute, 
  be 
  

   identified 
  by 
  the 
  unaided 
  eye. 
  They 
  are 
  usually 
  of 
  a 
  pale 
  

   colour, 
  and, 
  being 
  somewhat 
  thicker, 
  are 
  seen 
  distinctly 
  against 
  

   the 
  more 
  translucent 
  sheet 
  of 
  the 
  surrounding 
  pancreatic 
  

   alveoli. 
  Wherever 
  a 
  careful 
  search 
  was 
  made, 
  either 
  macro- 
  

   or 
  microscopically, 
  these 
  bodies 
  were 
  found, 
  and 
  hence 
  it 
  may 
  

   reasonably 
  be 
  concluded 
  they 
  constitute 
  a 
  common 
  feature 
  of 
  

  

  