﻿394 
  Mr. 
  Martin 
  E. 
  Mosely 
  on 
  

  

  its 
  surface 
  (PI. 
  XVIII, 
  fig. 
  4, 
  and 
  PL 
  XIX, 
  figs. 
  7 
  and 
  8). 
  

   Accompanying 
  this 
  form 
  of 
  scent-organ 
  are 
  to 
  be 
  found 
  

   two 
  tufts 
  of 
  scent-hairs, 
  similar 
  in 
  character 
  to 
  those 
  

   clothing 
  the 
  eversible, 
  tubular 
  filament 
  in 
  the 
  other 
  pattern. 
  

   The 
  tufts 
  originate 
  in 
  blunt, 
  membraneous 
  projections, 
  

   apparently 
  not 
  eversible, 
  situated 
  towards 
  the 
  inner 
  bases 
  

   of 
  the 
  lobes, 
  and 
  developing 
  out 
  of 
  a 
  membrane 
  which, 
  

   in 
  all 
  species 
  examined, 
  stretches 
  across 
  the 
  back 
  of 
  the 
  

   head 
  between 
  the 
  lobes. 
  

  

  Whether 
  all 
  these 
  varying 
  characters 
  should 
  rightly 
  be 
  

   described 
  as 
  scent-organs, 
  i. 
  e. 
  distributors 
  of 
  scent, 
  is 
  a 
  

   speculation 
  into 
  which 
  the 
  writer 
  is 
  not 
  prepared 
  to 
  enter, 
  

   but 
  it 
  appears 
  just 
  a 
  httle 
  curious 
  that 
  in 
  one 
  compara- 
  

   tively 
  small 
  order 
  such 
  as 
  the 
  Trichoptera 
  so 
  many 
  diverse 
  

   patterns 
  of 
  scent-organ 
  should 
  be 
  found, 
  varying 
  even 
  in 
  

   the 
  same 
  genus 
  according 
  to 
  the 
  species, 
  and 
  all 
  supposed 
  

   to 
  fulfil 
  the 
  same 
  function. 
  

  

  In 
  this 
  memoir 
  it 
  is 
  proposed 
  to 
  give 
  a 
  brief 
  description 
  

   of 
  the 
  scent-organs 
  of 
  some 
  of 
  the 
  species 
  of 
  Hydroptila, 
  

   and 
  it 
  will 
  be 
  seen 
  that 
  the 
  organs 
  furnish 
  reliable 
  characters 
  

   by 
  which 
  the 
  closely 
  resembling 
  species 
  of 
  the 
  sparsa 
  form 
  

   may 
  be 
  separated. 
  In 
  all 
  species 
  so 
  far 
  examined 
  the 
  head 
  

   is 
  furnished 
  with 
  two 
  lobes 
  varying 
  in 
  size 
  and 
  shape, 
  in 
  

   some 
  species 
  bi 
  valvular. 
  These 
  lobes 
  are 
  erectile, 
  are 
  

   sometimes 
  lined 
  with 
  scent-scales 
  (PI. 
  XIX, 
  fig. 
  10), 
  and 
  

   the 
  scent-organs 
  are 
  all 
  situated 
  beneath 
  them, 
  or 
  on 
  their 
  

   inner 
  surfaces. 
  When 
  a 
  tubular 
  filament 
  is 
  withdrawn 
  

   it 
  is 
  turned 
  outside 
  in, 
  like 
  the 
  finger 
  of 
  a 
  glove, 
  i. 
  e. 
  the 
  

   apex 
  is 
  returned 
  within 
  the 
  walls 
  of 
  the 
  filament, 
  so 
  that 
  

   when 
  partly 
  withdrawn 
  or 
  everted 
  there 
  is 
  formed 
  a 
  re- 
  

   entering 
  cup 
  at 
  the 
  extremity 
  (PI. 
  XVIII, 
  fig. 
  2). 
  When 
  

   a 
  filament 
  clothed 
  with 
  hairs 
  is 
  partially 
  extended 
  or 
  

   retracted, 
  the 
  hairs 
  are 
  gathered 
  together 
  and 
  protrude 
  

   from 
  the 
  hollowed 
  extremity 
  in 
  a 
  dense 
  yellow 
  or 
  black 
  

   brush, 
  according 
  to 
  the 
  species 
  (PI. 
  XVIII, 
  fig. 
  5, 
  and 
  

   PL 
  XIX, 
  figs. 
  9, 
  10, 
  and 
  11). 
  

  

  In 
  H. 
  femondis 
  this 
  brush 
  in 
  its 
  normal 
  position 
  rests 
  

   in 
  contact 
  with 
  the 
  scent-scales 
  lining 
  the 
  lobe, 
  and 
  no 
  

   doubt, 
  on 
  being 
  everted, 
  distributes 
  the 
  scent 
  collected 
  on 
  

   the 
  hairs 
  to 
  the 
  surrounding 
  atmosphere. 
  Possibly 
  this 
  

   arrangement 
  may 
  be 
  found 
  to 
  exist 
  in 
  other 
  species 
  as 
  

   well. 
  

  

  The 
  scent-organs 
  occur 
  in 
  the 
  male 
  sex 
  only. 
  

  

  