﻿102 
  Mr. 
  J, 
  W. 
  Douglas 
  o?? 
  the 
  

  

  and 
  advance 
  as 
  they 
  mine, 
  the 
  former 
  mine 
  all 
  round 
  the 
  place 
  

   they 
  inhabit 
  ; 
  this 
  place 
  is 
  marked 
  on 
  the 
  leaf 
  by 
  a 
  white 
  or 
  yel- 
  

   lowish 
  blotch, 
  being 
  in 
  fact 
  the 
  portion 
  of 
  the 
  leaf 
  that 
  has 
  been 
  de- 
  

   tached. 
  Had 
  this 
  portion 
  been 
  simply 
  loosened, 
  it 
  should 
  be 
  every 
  

   where 
  even 
  and 
  smooth, 
  as 
  when 
  it 
  was 
  attached 
  ; 
  consequently, 
  

   it 
  appeared 
  to 
  me 
  very 
  singular, 
  when 
  for 
  the 
  first 
  time 
  I 
  observed 
  

   on 
  a 
  portion 
  of 
  the 
  membrane 
  of 
  an 
  oak 
  leaf 
  a 
  ridge 
  (ariele) 
  pro- 
  

   jecting 
  above, 
  which 
  went 
  from 
  one 
  end 
  of 
  the 
  mined 
  place 
  to 
  the 
  

   end 
  diametrically 
  opposite. 
  It 
  was 
  at 
  first 
  natural 
  to 
  suppose 
  that 
  

   this 
  ridge 
  was 
  nothing 
  but 
  a 
  large 
  fibre 
  loosened 
  from 
  the 
  leaf; 
  

   but 
  its 
  direction 
  and 
  figure 
  destroyed 
  this 
  idea, 
  and 
  showed 
  that 
  

   it 
  was 
  not 
  a 
  fibre 
  of 
  the 
  plant. 
  I 
  have 
  since 
  constantly 
  observed 
  

   this 
  ridge 
  on 
  all 
  portions 
  of 
  the 
  epidermis 
  which 
  had 
  been 
  sepa- 
  

   rated 
  from 
  the 
  parenchyma 
  of 
  the 
  oak 
  leaves 
  by 
  certain 
  species 
  of 
  

   miners, 
  and 
  I 
  was 
  puzzled 
  how 
  it 
  could 
  be 
  produced, 
  till 
  I 
  ob- 
  

   served 
  the 
  mined 
  blotches 
  in 
  apple 
  and 
  elm 
  leaves. 
  These 
  mined 
  

   places 
  showed 
  me 
  why 
  the 
  loosened 
  epidermis 
  of 
  certain 
  oak 
  

   leaves 
  has 
  a 
  ridge, 
  what 
  is 
  the 
  use 
  of 
  this 
  ridge, 
  and 
  how 
  it 
  may 
  

   be 
  formed, 
  The 
  elm 
  leaf 
  miners 
  (^Lithocolleth 
  Schreherella) 
  are 
  of 
  

   the 
  largest 
  insects 
  of 
  this 
  kind, 
  yet 
  the 
  space 
  included 
  between 
  

   two 
  parallel 
  fibres 
  which 
  start 
  from 
  the 
  mid 
  rib 
  bound 
  the 
  space 
  

   in 
  which 
  each 
  excavates 
  and 
  feeds; 
  these 
  fibres 
  are 
  for 
  it 
  two 
  

   chains 
  of 
  mountains, 
  which 
  stop 
  it 
  on 
  each 
  side 
  ; 
  hence 
  it 
  makes 
  

   its 
  abode 
  longer 
  than 
  broad, 
  somewhat 
  oblong. 
  It 
  is 
  the 
  lower 
  

   epidermis 
  of 
  the 
  leaf 
  which 
  it 
  first 
  loosens, 
  and 
  it 
  afterwards 
  eats 
  

   all 
  the 
  pulp 
  that 
  is 
  between 
  this 
  and 
  the 
  upper 
  epidermis. 
  In- 
  

   stead 
  of 
  one 
  ridge, 
  such 
  as 
  I 
  had 
  seen 
  on 
  the 
  oak 
  leaves, 
  I 
  have 
  

   often 
  seen 
  two 
  or 
  three, 
  and 
  sometimes 
  nriore, 
  on 
  the 
  loosened 
  

   epidermis 
  of 
  an 
  elm 
  leaf. 
  The 
  structure 
  of 
  each 
  of 
  these 
  was 
  

   easier 
  to 
  recognize 
  than 
  that 
  of 
  those 
  of 
  the 
  oak 
  ; 
  it 
  was 
  evident 
  

   that 
  each 
  was 
  only 
  a 
  fold 
  of 
  the 
  epidermis, 
  and 
  that 
  the 
  summit 
  of 
  

   the 
  fold 
  which 
  rose 
  above 
  the 
  rest 
  formed 
  the 
  ridge 
  in 
  question 
  ; 
  

   this 
  was 
  shown 
  in 
  tracing 
  each 
  ridge 
  from 
  one 
  end 
  to 
  the 
  other, 
  

   because 
  towards 
  one 
  end 
  were 
  seen 
  the 
  two 
  portions 
  of 
  the 
  epi- 
  

   dermis 
  which 
  began 
  to 
  curve 
  towards 
  each 
  other, 
  and 
  a 
  little 
  

   further 
  they 
  were 
  almost 
  contiguous, 
  whence 
  it 
  was 
  easy 
  to 
  judge 
  

   that 
  in 
  the 
  rest 
  of 
  their 
  extent 
  they 
  were 
  applied 
  exactly 
  one 
  

   against 
  the 
  other. 
  

  

  " 
  The 
  effect 
  produced 
  by 
  these 
  folds 
  of 
  the 
  membrane 
  is 
  evi- 
  

   dent, 
  they 
  contract 
  it, 
  and 
  consequently 
  force 
  the 
  fibres 
  to 
  which 
  

   it 
  is 
  attached 
  to 
  approach 
  each 
  other 
  ; 
  tlie 
  opposite 
  membrane 
  on 
  

   which 
  the 
  substance 
  of 
  the 
  leaf 
  rests 
  is 
  also 
  thereby 
  compelled 
  to 
  

   curve 
  and 
  become 
  convex 
  on 
  the 
  outside 
  of 
  the 
  leaf. 
  The 
  advan- 
  

   tage 
  to 
  the 
  insect 
  is 
  apparent 
  ; 
  it 
  obtains 
  a 
  tenement 
  of 
  greater 
  

  

  