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  beetle, 
  Hydrophilus 
  piceus. 
  The 
  results 
  of 
  my 
  investigations 
  were 
  after- 
  

   wards 
  published 
  in 
  Paris. 
  244 
  A 
  few 
  months 
  later 
  Graber 
  also 
  described 
  

   the 
  structure 
  of 
  the 
  tracheae, 
  pointing 
  out 
  Leydig's 
  error. 
  Graber's 
  ob- 
  

   servations 
  are 
  published 
  incidentally 
  in 
  his 
  article 
  on 
  the 
  tympanal 
  

   organs 
  of 
  the 
  Orthoptera. 
  245 
  

  

  I 
  have 
  found 
  that 
  the 
  account 
  I 
  then 
  published 
  of 
  the 
  minute 
  anatomy 
  

   of 
  the 
  air 
  tubes 
  in 
  Hydrophilus 
  is 
  applicable, 
  almost 
  without 
  change, 
  to 
  

   the 
  grasshoppers, 
  and 
  I 
  have, 
  moreover, 
  been 
  able 
  to 
  convince 
  myself 
  

   that 
  the 
  epithelium 
  is 
  not 
  columnar, 
  but 
  a 
  true 
  pavement 
  epithelium 
  

   ( 
  Pflasterepithel) 
  as 
  I 
  had 
  previously 
  found 
  it 
  to 
  be 
  in 
  Hydropliilus 
  and 
  

   other 
  insects. 
  My 
  own 
  observations 
  certainly 
  imply 
  that 
  Dr. 
  Chun 
  is 
  

   in 
  error 
  as 
  to 
  the 
  nature 
  of 
  this 
  layer 
  in 
  those 
  species 
  that 
  he 
  examined. 
  

   In 
  order 
  to 
  avoid 
  repetition 
  I 
  reproduce 
  here 
  a 
  figure 
  (7) 
  of 
  a 
  longitudi- 
  

   nal 
  section 
  of 
  a 
  trachea 
  of 
  the 
  European 
  water 
  beetle, 
  taken 
  from 
  the 
  

   American 
  Naturalist, 
  July, 
  1877. 
  Externally 
  lies 
  the 
  

   epithelium 
  cp, 
  which 
  is 
  readily 
  recognized 
  by 
  the 
  flat- 
  

   tened 
  elongated 
  nuclei. 
  Next 
  follows 
  the 
  inner 
  layer 
  of 
  

   the 
  cuticula, 
  cu, 
  and 
  interiorly 
  the 
  darker 
  colored 
  inner 
  

   layer, 
  in 
  which 
  are 
  imbedded 
  the 
  dark 
  colored 
  spiral 
  fila- 
  

   ments/. 
  This 
  arrangement 
  recurs 
  in 
  a 
  number 
  of 
  in- 
  

   sects 
  and 
  probably 
  in 
  all, 
  the 
  variations 
  being 
  merely 
  

   in 
  the 
  proportionate 
  thicknesses 
  of 
  the 
  various 
  parts, 
  

   and 
  the 
  relative 
  size 
  of 
  the 
  spiral 
  threads. 
  

  

  If 
  short 
  pieces 
  of 
  the 
  tracheae 
  be 
  pulled 
  out, 
  then 
  

  

  stained 
  with 
  carmine 
  or 
  haematoxiline 
  and 
  mounted, 
  it 
  

  

  8 
  g 
  ecti^n°of 
  gl 
  ilrg 
  a 
  e 
  wu 
  l 
  be 
  noticed 
  that 
  the 
  size 
  of 
  the 
  spiral 
  filaments, 
  and 
  

  

  trache® 
  of 
  Hydro- 
  also 
  the 
  distance 
  between 
  them, 
  diminishes 
  with 
  the 
  

  

  phttus 
  piceus. 
  g 
  - 
  ze 
  Q 
  £ 
  ^ 
  e 
  toache®. 
  Where 
  a 
  smaller 
  trachea 
  springs 
  

  

  from 
  a 
  larger 
  one, 
  there 
  is 
  not 
  a 
  gradual 
  passage 
  from 
  the 
  large 
  to 
  the 
  

  

  small 
  threads, 
  but 
  at 
  the 
  point 
  of 
  origin 
  the 
  filaments 
  of 
  the 
  large 
  

  

  tracheae 
  bend 
  apart 
  so 
  as 
  to 
  leave 
  a 
  space 
  in 
  which 
  the 
  tracheal 
  branch 
  

  

  takes 
  rise, 
  beginning 
  at 
  once 
  with 
  small 
  spiral 
  threads. 
  

  

  The 
  preparations 
  we 
  are 
  now 
  considering 
  further 
  show 
  that 
  there 
  is 
  

   not 
  a 
  single 
  spiral 
  thread, 
  but 
  several, 
  which 
  run 
  parallel 
  to 
  one 
  another, 
  

   as 
  I 
  have 
  shown 
  before 
  246 
  , 
  and 
  end 
  after 
  making 
  a 
  few 
  turns 
  around 
  the 
  

   trachea. 
  The 
  single 
  threads 
  terminate 
  not 
  abruptly 
  but 
  by 
  tapering 
  

   down 
  to 
  a 
  point 
  and 
  so 
  disappearing. 
  

  

  The 
  nuclei 
  (Figs. 
  8 
  and 
  61) 
  of 
  the 
  tracheal 
  epithelium 
  are 
  elliptical 
  in 
  

   outline, 
  much 
  flattened, 
  though 
  considerably 
  thicker 
  than 
  the 
  body 
  of 
  

   the 
  cells. 
  Their 
  long 
  axis 
  is 
  more 
  or 
  less 
  nearly 
  parallel 
  with 
  that 
  of 
  the 
  

   trachea, 
  and 
  they 
  all 
  have 
  a 
  very 
  distinct 
  and 
  highly 
  refringent 
  nucleo- 
  

   lus 
  j 
  sometimes 
  two. 
  The 
  nucleoli 
  are, 
  I 
  believe, 
  always 
  eccentrically 
  

  

  244 
  Archives 
  de 
  Phyaiologie 
  Normale 
  et 
  Pathologique, 
  1876, 
  p. 
  1, 
  and 
  in 
  Ranvier's 
  Travaux 
  dn 
  Labora- 
  

   toire, 
  etc., 
  1876, 
  p. 
  1. 
  

  

  *» 
  Graber: 
  Bonk. 
  Wien. 
  Akad, 
  xxxvi, 
  p. 
  35. 
  

  

  WMinot: 
  Recherches 
  histologiques 
  sur 
  lea 
  Trachees 
  de 
  l'Hydrophilus 
  picoua. 
  Arch, 
  de 
  Physiol, 
  

   expt. 
  1876, 
  p. 
  1. 
  

  

  