﻿384 
  

  

  Mr. 
  T. 
  E. 
  Thorpe 
  on 
  the 
  

  

  [Apr. 
  15_, 
  

  

  Prof. 
  Huxley 
  first 
  correctly 
  determined 
  the 
  homologies 
  of 
  the 
  enamel- 
  

   organ 
  and 
  the 
  dentine-papilla, 
  referring 
  the 
  first 
  to 
  the 
  epithelium, 
  the 
  

   latter 
  to 
  the 
  derm 
  ; 
  the 
  follicle, 
  however, 
  where 
  it 
  exists 
  at 
  all, 
  I 
  regard 
  

   as 
  mainly 
  a 
  secondary 
  development 
  from 
  that 
  region 
  of 
  the 
  derm 
  which 
  

   formed 
  the 
  base 
  of 
  the 
  dentine-germ. 
  

  

  Observations 
  upon 
  many 
  mammals, 
  reptiles, 
  and 
  fishes 
  lead 
  me 
  to 
  

   the 
  following 
  general 
  conclusions 
  as 
  to 
  the 
  development 
  of 
  teeth 
  : 
  — 
  

  

  (i.) 
  All 
  tooth-germs 
  whatever 
  consist, 
  in 
  the 
  first 
  instance, 
  of 
  two 
  

   parts, 
  and 
  two 
  alone 
  — 
  the 
  dentine-papilla 
  and 
  the 
  enamel- 
  organ. 
  

  

  (ii.) 
  The 
  existence 
  of 
  an 
  enamel-organ 
  is 
  wholly 
  independent 
  of 
  the 
  

   presence 
  or 
  absence 
  of 
  enamel 
  upon 
  the 
  teeth 
  ; 
  examples 
  of 
  this 
  have 
  

   been 
  recorded 
  by 
  Professor 
  Turner 
  and 
  by 
  myself 
  among 
  mammalia, 
  

   and 
  by 
  myself 
  among 
  reptiles 
  and 
  fishes. 
  

  

  (iii.) 
  Nothing 
  justifies 
  the 
  arbitrary 
  division 
  into 
  " 
  papillary," 
  " 
  folli- 
  

   cular," 
  and 
  " 
  eruptive" 
  stages 
  ; 
  nor 
  does 
  any 
  open 
  primitive 
  dental 
  groove, 
  

   or 
  fissure, 
  exist 
  in 
  any 
  animal 
  examined. 
  

  

  (iv.) 
  In 
  all 
  cases, 
  an 
  active 
  ingrowth 
  of 
  a 
  process 
  of 
  the 
  oral 
  epi- 
  

   thelium, 
  dipping 
  inwards 
  into 
  solid 
  tissue, 
  is 
  the 
  first 
  thing 
  distinguish- 
  

   able 
  ; 
  although 
  the 
  formation 
  of 
  a 
  dentine-papilla, 
  opposite 
  to 
  its 
  deepest 
  

   extremity, 
  goes 
  on 
  pari 
  passu 
  with 
  the 
  development 
  of 
  its 
  caecal 
  end 
  into 
  

   an 
  enamel-organ. 
  

  

  (v.) 
  A 
  special 
  capsule, 
  or 
  follicle, 
  to 
  the 
  tooth-germ 
  may 
  or 
  may 
  not 
  

   be 
  present 
  ; 
  when 
  present, 
  it 
  is, 
  in 
  part, 
  a 
  secondary 
  development 
  from 
  

   the 
  base 
  of 
  the 
  dentine-papilla, 
  in 
  part, 
  a 
  mere 
  condensation 
  of 
  sur- 
  

   rounding 
  tissue. 
  

  

  IT. 
  " 
  Researches 
  upon 
  the 
  Specific 
  Volumes 
  of 
  Liquids.-'-' 
  By 
  T. 
  

   E. 
  Thorpe. 
  Communicated 
  by 
  Prof. 
  Williamson, 
  For. 
  Sec. 
  

   U.S. 
  Received 
  March 
  2, 
  1875. 
  

  

  (Abstract.) 
  

  

  I. 
  0)i 
  the 
  Atomic 
  Value 
  of 
  Plwsjphorus. 
  

  

  Hermann 
  Kopp 
  has 
  shown 
  that, 
  as 
  a 
  rule, 
  the 
  specific 
  volume 
  of 
  an 
  ele- 
  

   ment 
  is 
  invariable 
  when 
  in 
  combination. 
  Exceptions 
  to 
  the 
  law 
  occur, 
  

   however, 
  in 
  the 
  cases 
  of 
  oxygen 
  and 
  sulphur, 
  each 
  of 
  which 
  bodies 
  has 
  

   two 
  specific 
  volumes 
  dependent 
  upon 
  the 
  manner 
  in 
  which 
  they 
  are 
  held 
  in 
  

   union. 
  "When 
  contained 
  " 
  within 
  the 
  radicle," 
  as 
  in 
  acetyl, 
  C 
  2 
  H 
  3 
  0, 
  oxygen 
  

   has 
  the 
  value 
  12-2, 
  but 
  when 
  existing 
  "without 
  the 
  radicle," 
  as 
  in 
  alcohol, 
  

   it 
  has 
  the 
  smaller 
  value, 
  7*8. 
  Sulphur, 
  when 
  " 
  within 
  the 
  radicle," 
  has 
  the 
  

   specific 
  volume 
  28-6 
  ; 
  when 
  " 
  without 
  the 
  radicle,'' 
  it 
  has 
  the 
  specific 
  

   volume 
  22' 
  6. 
  

  

  The 
  cause 
  of 
  these 
  variations 
  may 
  be 
  thus 
  stated 
  in 
  the 
  language 
  of 
  

   modern 
  theory 
  :■ 
  — 
  "When 
  dyad 
  sulphur 
  and 
  oxygen 
  are 
  united 
  to 
  an 
  ele- 
  

   ment 
  by 
  both 
  their 
  affinities. 
  3 
  their 
  specific 
  volumes 
  become 
  respectively 
  

  

  