﻿the 
  Hessian 
  Fly. 
  337 
  

  

  Perhaps 
  it 
  will 
  not 
  be 
  waste 
  of 
  time 
  to 
  consider 
  the 
  

   position 
  of 
  the 
  larva 
  when 
  feeding. 
  The 
  head 
  and 
  

   mouth-organs 
  of 
  a 
  new-born 
  larva 
  are, 
  as 
  you 
  will 
  see 
  

   from 
  the 
  photograph, 
  placed 
  at 
  the 
  extreme 
  end 
  ; 
  but 
  if 
  

   we 
  examine 
  a 
  full-grown 
  larva, 
  we 
  find 
  the 
  head 
  has 
  

   become 
  invaginated 
  and 
  bent 
  round 
  almost 
  at 
  right 
  

   angles 
  to 
  the 
  body, 
  so 
  as 
  to 
  bring 
  the 
  mouth-organs 
  into 
  

   contact 
  with 
  the 
  stalk 
  of 
  the 
  plant, 
  and 
  as 
  the 
  juices 
  

   are 
  imbibed 
  the 
  cells 
  become 
  partially 
  withered, 
  forming 
  

   a 
  cavity 
  in 
  the 
  stalk, 
  in 
  which 
  the 
  larva 
  is 
  embedded, 
  or 
  

   pressed 
  into, 
  by 
  the 
  encircling 
  leaf-sheath. 
  

  

  I 
  must 
  confess 
  that 
  when 
  I 
  read 
  that 
  the 
  larva 
  fixes 
  

   itself 
  head 
  doivnivards, 
  I 
  felt 
  rather 
  incredulous, 
  for 
  I 
  im- 
  

   mediately 
  thought, 
  if 
  this 
  be 
  so, 
  How 
  does 
  the 
  flij 
  emerge 
  ? 
  

   for, 
  as 
  you 
  see 
  from 
  the 
  photograph 
  (Plate 
  XVI., 
  fig. 
  9), 
  

   the 
  head 
  of 
  the 
  larva 
  is 
  doivnivards 
  and 
  turned 
  iinvards, 
  

   fixed 
  into 
  the 
  solid 
  stem 
  ; 
  and, 
  even 
  supposing 
  that 
  the 
  

   pupa 
  was 
  capable 
  of 
  penetrating 
  this, 
  it 
  would 
  only 
  land 
  

   itself 
  in 
  the 
  centre 
  of 
  the 
  hollow 
  stem, 
  with 
  a 
  solid 
  joint 
  

   top 
  and 
  bottom 
  to 
  bar 
  further 
  progress. 
  I 
  then 
  thought 
  

   that 
  surely 
  the 
  larva 
  must, 
  as 
  soon 
  as 
  it 
  reaches 
  the 
  joint, 
  

   immediately 
  reverse 
  its 
  position, 
  keeping 
  its 
  head 
  tqj, 
  and 
  

   then 
  there 
  would 
  be 
  no 
  impediment 
  in 
  the 
  way 
  of 
  the 
  fly 
  

   when 
  emerging. 
  I 
  examined 
  a 
  number 
  of 
  half-grown 
  

   larvse 
  most 
  carefully, 
  and 
  could 
  not 
  then 
  come 
  to 
  any 
  

   other 
  conclusion 
  but 
  that 
  they 
  had 
  been 
  wrongly 
  described 
  

   as 
  having 
  their 
  heads 
  downwards, 
  and 
  this 
  idea 
  was 
  

   considerably 
  strengthened 
  when 
  I 
  bred 
  several 
  of 
  the 
  

   flies, 
  for 
  on 
  examination 
  of 
  the 
  puparia 
  I 
  found 
  they 
  had 
  

   emerged 
  at 
  the 
  top 
  end 
  

  

  On 
  Sept. 
  6th, 
  1888, 
  I 
  examined 
  some 
  of 
  the 
  home- 
  

   grown 
  barley 
  plants, 
  and 
  found 
  six 
  larvae 
  at 
  one 
  joint 
  ; 
  

   one 
  of 
  them 
  was 
  full 
  grown, 
  the 
  colour 
  glassy-white, 
  with 
  

   the 
  usual 
  greenish 
  intestine, 
  the 
  skin 
  perfectly 
  tight, 
  so 
  

   that 
  the 
  segments 
  were 
  scarcely 
  visible. 
  I 
  laid 
  this 
  

   specimen 
  on 
  its 
  back 
  for 
  the 
  purpose 
  of 
  making 
  an 
  exact 
  

   drawing, 
  and, 
  whilst 
  engaged 
  measuring 
  the 
  lower 
  or 
  

   thick 
  end 
  with 
  the 
  eye-piece 
  micrometer, 
  I 
  was 
  astonished 
  

   to 
  see 
  through 
  the 
  skin, 
  immediately 
  below 
  the 
  orifice 
  

   (which 
  I 
  had 
  imagined 
  was 
  the 
  tail), 
  the 
  anchor-process 
  

   in 
  motion. 
  This 
  discovery 
  — 
  to 
  use 
  a 
  somewhat 
  un- 
  

   scientific 
  expression 
  — 
  "sent 
  my 
  heart 
  into 
  my 
  mouth,'' 
  

   for 
  I 
  had 
  a 
  strange 
  feeling 
  that 
  I 
  was 
  on 
  the 
  point 
  of 
  

   clearing 
  up 
  a 
  great 
  difdculty 
  ; 
  for 
  as 
  this 
  apparatus, 
  the 
  

  

  