﻿Scent-organs 
  in 
  the 
  genus 
  Hgdroptila. 
  395 
  

  

  Description 
  of 
  Scent-organs. 
  

  

  Hydroptila 
  sparsa 
  Curt. 
  (PI. 
  XVIII, 
  figs. 
  1, 
  2, 
  and 
  3). 
  

  

  The 
  scent-organ 
  consists 
  of 
  four 
  eversible, 
  tubular 
  

   filaments 
  arising 
  from 
  a 
  membrane 
  extending 
  across 
  the 
  

   back 
  of 
  the 
  head, 
  between 
  the 
  lobes. 
  Although 
  an 
  ex- 
  

   amination 
  has 
  been 
  made 
  of 
  a 
  large 
  number 
  of 
  individuals, 
  

   I 
  have 
  as 
  yet 
  found 
  no 
  clear 
  trace 
  of 
  scent-hairs. 
  Two 
  

   small 
  groups 
  of 
  battledore 
  scales 
  are 
  attached 
  to 
  the 
  

   membrane 
  towards 
  the 
  bases 
  of 
  the 
  filaments. 
  These 
  

   scales 
  difier 
  in 
  shape 
  from 
  those 
  of 
  the 
  other 
  species, 
  

   having 
  greatly 
  elongated 
  foot-stalks. 
  

  

  The 
  lobes 
  appear 
  to 
  be 
  merely 
  bi-valvular 
  caps, 
  covering 
  

   the 
  membrane 
  when 
  the 
  filaments 
  arc 
  withdrawn. 
  

  

  Hydroptila 
  siraulans 
  Mosely 
  (PI. 
  XVIII, 
  figs. 
  5 
  and 
  G). 
  

  

  There 
  are 
  two 
  eversible, 
  tubular 
  filaments 
  clothed 
  with 
  

   golden-yellow 
  hairs. 
  I 
  have 
  not 
  been 
  able 
  to 
  satisfy 
  

   myself 
  as 
  to 
  the 
  presence 
  or 
  absence 
  of 
  scales 
  on 
  the 
  inner 
  

   surfaces 
  of 
  the 
  lobes, 
  which 
  have 
  somewhat 
  the 
  appearance 
  

   of 
  longitudinally 
  bisected 
  acorns 
  with 
  roughened 
  inner 
  

   surfaces. 
  

  

  Hydroptila 
  forcipata 
  Eaton 
  (PI. 
  XIX, 
  figs. 
  7 
  and 
  8). 
  

  

  The 
  lobes 
  are 
  very 
  narrow, 
  and 
  each 
  is 
  lined 
  with 
  a 
  

   membrane 
  capable 
  of 
  considerable 
  dilatation. 
  There 
  is 
  a 
  

   ring 
  of 
  rather 
  narrow 
  striated 
  battledore 
  scales 
  towards 
  

   the 
  junction 
  of 
  this 
  membrane 
  with 
  the 
  margin 
  of 
  the 
  

   lobe. 
  A 
  membrane 
  extends 
  across 
  the 
  back 
  of 
  the 
  head 
  

   connecting 
  the 
  two 
  lobes. 
  Towards 
  the 
  base 
  of 
  each 
  lobe 
  

   there 
  is 
  a 
  shght 
  swelling 
  in 
  this 
  membrane, 
  from 
  which 
  

   arises 
  a 
  bunch 
  of 
  scent-hairs, 
  but 
  there 
  does 
  not 
  appear 
  

   to 
  be 
  any 
  eversible 
  filament. 
  

  

  Hydroptila 
  maclachlani 
  Klap 
  (PI. 
  XVIII, 
  fig. 
  4). 
  

  

  In 
  this 
  species 
  the 
  scent-organ 
  seems 
  similar 
  in 
  construc- 
  

   tion 
  to 
  that 
  of 
  H. 
  forcipata. 
  The 
  scales 
  on 
  the 
  membrane 
  

   may 
  perhaps 
  be 
  fewer 
  in 
  number, 
  and 
  the 
  scent-hairs 
  are 
  

   inserted 
  in 
  funnel-shaped 
  sockets. 
  The 
  lobes 
  are 
  even 
  

   more 
  narrow 
  than 
  in 
  H. 
  forcipata, 
  and 
  when 
  in 
  their 
  normal 
  

   position 
  are 
  pressed 
  flat 
  against 
  the 
  back 
  of 
  the 
  head, 
  

   inclining 
  towards 
  each 
  other 
  and 
  nearly 
  invisible 
  without 
  

   the 
  aid 
  of 
  a 
  powerful 
  lens. 
  

  

  