﻿218 
  Report 
  united 
  states 
  entomological 
  commission. 
  

  

  and, 
  like 
  that 
  on 
  the 
  ileum, 
  it 
  rests 
  upon 
  a 
  layer 
  of 
  connective 
  tissue, 
  

   beyond 
  which 
  follows 
  (1) 
  an 
  internal 
  coat 
  of 
  longitudinal, 
  and 
  (2) 
  an 
  ex- 
  

   ternal 
  coat 
  of 
  circular 
  muscular 
  fibres, 
  which 
  are 
  striated. 
  

  

  Rectum. 
  — 
  The 
  rectum 
  of 
  insects 
  is 
  remarkable 
  for 
  containing 
  certain 
  

   curious 
  structures 
  now 
  generally 
  known 
  as 
  rectal 
  glands. 
  They 
  are 
  in- 
  

   cidentally 
  mentioned 
  by 
  older 
  authors, 
  but 
  Frey 
  and 
  Leuckart 
  309 
  were, 
  as 
  

   far 
  as 
  I 
  am 
  aware, 
  the 
  first 
  to 
  recognize 
  their 
  general 
  distribution 
  and 
  

   importance. 
  Ley 
  dig 
  310 
  was 
  the 
  first 
  to 
  give 
  an 
  accurate 
  account 
  of 
  their 
  

   histological 
  structure. 
  Since 
  then 
  they 
  have 
  received 
  but 
  little 
  atten- 
  

   tion 
  until 
  1876, 
  when 
  Dr. 
  Ohun 
  published 
  his 
  investigations, 
  311 
  which 
  were 
  

   made 
  under 
  the 
  guidance 
  of 
  Professor 
  Leuckart. 
  Ohun 
  extended 
  his 
  

   researches 
  over 
  a 
  variety 
  of 
  insects, 
  but 
  gives 
  no 
  account 
  of 
  the 
  glands 
  

   as 
  found 
  in 
  the 
  grasshoppers, 
  though 
  he 
  studied 
  the 
  closely 
  allied 
  Katy- 
  

   did 
  (Locusta 
  viridissima, 
  1. 
  c, 
  p. 
  32). 
  He 
  describes 
  the 
  glands 
  as 
  six 
  flat 
  

   folds, 
  formed 
  by 
  a 
  high 
  epithelium 
  and 
  well-defined 
  cuticula; 
  the 
  con- 
  

   nective 
  tissue 
  (tunica 
  propria) 
  is 
  largely 
  predominant 
  ; 
  there 
  is 
  a 
  coat 
  of 
  

   circular 
  muscular 
  fibers, 
  and 
  six 
  external 
  longitudinal 
  muscular 
  bands, 
  

   corresponding 
  to 
  the 
  furrows 
  between 
  the 
  glands. 
  This 
  description 
  is 
  

   applicable 
  also 
  to 
  the 
  grasshoppers 
  I 
  have 
  investigated, 
  the 
  only 
  differ- 
  

   ences 
  being 
  in 
  the 
  structural 
  details 
  of 
  the 
  single 
  layers. 
  

  

  Seen 
  from 
  the 
  inner 
  surface 
  the 
  epithelium 
  presents 
  a 
  most 
  curious 
  

   and 
  puzzling 
  aspect, 
  Fig. 
  53, 
  because 
  there 
  are 
  two 
  kinds 
  of 
  nuclei 
  

   at 
  different 
  levels; 
  small, 
  spherical 
  nuclei 
  nearest 
  the 
  surface, 
  and 
  

   larger 
  nuclei 
  of 
  oval 
  form 
  deeper 
  down. 
  The 
  small 
  nuclei 
  are 
  less 
  

   numerous 
  than 
  the 
  large 
  ; 
  in 
  the 
  portion 
  represented 
  in 
  Fig. 
  48 
  there 
  

   are 
  21 
  small 
  aud 
  49 
  large 
  nuclei, 
  or, 
  in 
  other 
  words, 
  less 
  than 
  half 
  as 
  

   many 
  of 
  the 
  superficial 
  as 
  of 
  the 
  deep 
  nuclei. 
  As 
  the 
  two 
  sets 
  are 
  at 
  

   different 
  levels 
  they 
  cannot 
  both 
  be 
  in 
  focus 
  at 
  once, 
  hence 
  in 
  drawing 
  

   Fig. 
  53 
  with 
  the 
  camera-lucida, 
  the 
  large 
  nuclei 
  were 
  first 
  focused 
  

   and 
  drawn, 
  and 
  then 
  the 
  smaller 
  nuclei 
  were 
  drawn 
  in 
  the 
  same 
  way 
  

   over 
  the 
  first. 
  When 
  we 
  focus 
  upon 
  the 
  large 
  nuclei, 
  the 
  polygonal 
  

   outlines 
  of 
  the 
  cells 
  can 
  be 
  seen 
  in 
  successful 
  preparations 
  as 
  repre- 
  

   sented 
  in 
  the 
  figure 
  ; 
  as 
  there 
  are 
  no 
  spaces 
  between 
  the 
  cells 
  with 
  the 
  

   large 
  nuclei, 
  the 
  cells 
  belonging 
  to 
  the 
  small 
  nuclei 
  do 
  not 
  extend 
  so 
  far 
  

   down, 
  though 
  the 
  cells 
  of 
  the 
  large 
  nuclei 
  do 
  reach 
  up 
  among 
  the 
  small 
  

   nuclei, 
  as 
  can 
  be 
  seen 
  in 
  sections. 
  The 
  outlines 
  of 
  the 
  cells 
  to 
  which 
  the 
  

   small 
  nuclei 
  belong, 
  I 
  have 
  not 
  been 
  able 
  to 
  distinguish. 
  

  

  The 
  small 
  nuclei 
  are 
  spherical, 
  very 
  refringent, 
  and 
  have 
  a 
  sharp 
  out- 
  

   line. 
  The 
  large 
  nuclei 
  are 
  oval, 
  their 
  long 
  axes 
  lying 
  generally 
  length- 
  

   wise 
  rather 
  than 
  transversely 
  on 
  the 
  folds 
  of 
  the 
  rectum. 
  An 
  epithelium 
  

   presenting 
  a 
  somewhat 
  analogous 
  peculiarity 
  has 
  been 
  described 
  from 
  

   the 
  epididymis 
  of 
  mammals 
  by 
  Klein. 
  312 
  He 
  figures 
  small 
  darkly 
  stained 
  

  

  309 
  Frey 
  and 
  Leuckart: 
  TJebersicbt 
  des 
  Thierroichs, 
  1855, 
  p. 
  11G. 
  

  

  810 
  Ley 
  'dig 
  : 
  Lehrbuch 
  der 
  Uistologie, 
  p. 
  337. 
  

  

  311 
  0. 
  Ohun: 
  Ueber 
  den 
  Bau, 
  die 
  Entwickelung 
  und 
  physiologische 
  Eedeutung 
  der 
  Rectaldriisen 
  bei 
  

   den 
  Insecten. 
  Abh. 
  : 
  Senckb. 
  Natforseh. 
  Gos. 
  (Frankfort) 
  Bd. 
  x, 
  p. 
  27, 
  mit 
  drei 
  Tafeln. 
  

  

  812 
  Klein: 
  Observations 
  on 
  the 
  structure 
  of 
  cells 
  and 
  nuclei. 
  Quart. 
  Journ. 
  Micros. 
  Sci., 
  XIX, 
  (1870), 
  

   p. 
  138, 
  pi. 
  VII, 
  fig. 
  9. 
  

  

  