﻿Histology 
  of 
  the 
  Scent-orgavis 
  in 
  the 
  Genus 
  Hydroptila. 
  425 
  

  

  has 
  a 
  peculiar 
  structure 
  as 
  though 
  formed 
  of 
  minute 
  

   chitinous 
  plates, 
  giving 
  it 
  somewhat 
  the 
  appearance 
  of 
  a 
  

   tessellated 
  pavement. 
  The 
  thicker 
  basal 
  portion 
  of 
  the 
  

   lobe 
  shows 
  in 
  section 
  a 
  hning 
  of 
  hypodermal 
  cells 
  probably 
  

   of 
  a 
  glandular 
  nature. 
  Beneath 
  the 
  lobes 
  and 
  directed 
  

   upwards 
  and 
  centrally 
  are 
  two 
  brushes 
  formed 
  of 
  a 
  mass 
  

   of 
  golden 
  yellow 
  hairs 
  arising 
  from 
  small 
  sockets 
  in 
  the 
  

   hning 
  of 
  a 
  brush 
  bag, 
  the 
  whole 
  presenting 
  an 
  arrangement 
  

   and 
  appearance 
  closely 
  resembling 
  that 
  in 
  many 
  Danaine 
  

   butterflies. 
  A 
  section 
  through 
  the 
  head 
  in 
  the 
  plane 
  of 
  

   the 
  long 
  axes 
  of 
  the 
  two 
  brushes 
  is 
  shown 
  at 
  fig. 
  8. 
  From 
  

   this 
  it 
  will 
  be 
  seen 
  that 
  the 
  hairs 
  arise 
  over 
  nearly 
  the 
  whole 
  

   length 
  of 
  the 
  bag, 
  and 
  hence 
  when 
  the 
  latter 
  is 
  everted 
  the 
  

   appearance 
  is 
  somewhat 
  that 
  of 
  a 
  test-tube 
  brush 
  or 
  pipe 
  

   cleaner. 
  The 
  hairs 
  are 
  slightly 
  thickened 
  towards 
  their 
  

   distal 
  extremities. 
  In 
  the 
  substance 
  of 
  the 
  bag 
  are 
  two 
  

   distinct 
  layers, 
  the 
  inner 
  one 
  being 
  thin 
  chitin 
  thrown 
  

   into 
  a 
  multiphcity 
  of 
  folds 
  and 
  bearing 
  the 
  sockets 
  of 
  the 
  

   hairs. 
  These 
  sockets 
  are 
  of 
  pecuhar 
  formation, 
  and 
  

   resemble 
  the 
  structures 
  laiown 
  to 
  botanists 
  as 
  bracts. 
  

   Outside 
  this 
  membranous 
  layer 
  is 
  a 
  glandular 
  epithelium 
  

   consisting 
  of 
  granulated 
  and 
  heavily 
  nucleated 
  cells 
  shown 
  

   in 
  fig. 
  10. 
  

  

  The 
  hairs 
  themselves 
  are 
  not 
  smooth, 
  but 
  have 
  an 
  

   elaborate 
  structure 
  which 
  I 
  have 
  endeavoured 
  to 
  represent 
  

   in 
  fig. 
  9. 
  There 
  are 
  whorls 
  of 
  laminate 
  projections 
  having 
  

   irregularly 
  curved 
  distal 
  margins. 
  Also 
  the 
  projections 
  

   are 
  not 
  continuous 
  round 
  the 
  hair, 
  but 
  the 
  rings 
  are 
  inter- 
  

   cepted 
  at 
  irregular 
  intervals 
  by 
  more 
  or 
  less 
  vertical 
  fissures. 
  

   The 
  elaborate 
  structure 
  of 
  the 
  minute 
  brush 
  hairs 
  in 
  this 
  

   and 
  other 
  species 
  is 
  one 
  of 
  the 
  most 
  notable 
  features 
  of 
  the 
  

   scent-organs. 
  

  

  The 
  general 
  arrangement 
  in 
  H. 
  simulans 
  seems 
  to 
  be 
  

   analogous 
  to 
  that 
  in 
  the 
  butterflies 
  Trepsichrois 
  mulciber 
  

   and 
  Hestia 
  lynceus, 
  in 
  which 
  the 
  brush 
  hairs 
  themselves 
  

   are 
  the 
  direct 
  vehicles 
  of 
  a 
  secretion 
  produced 
  by 
  glands 
  at 
  

   the 
  bases 
  of 
  their 
  sockets. 
  Fig. 
  7 
  is 
  a 
  view 
  of 
  the 
  head 
  

   with 
  the 
  lobes 
  closed. 
  

  

  H. 
  forcipata 
  Eaton. 
  

  

  In 
  this 
  species 
  the 
  lobes 
  are 
  very 
  small 
  as 
  is 
  the 
  whole 
  

   area 
  of 
  the 
  scent-organs. 
  Fig. 
  15 
  is 
  a 
  view 
  of 
  the 
  posterior 
  

   surface 
  of 
  the 
  head 
  with 
  the 
  lobes 
  turned 
  back. 
  Here 
  we 
  

  

  