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  writhes 
  in 
  a 
  way 
  to 
  endanger 
  the 
  delicate 
  larva, 
  which 
  recoils 
  until 
  

   its 
  prey 
  regains 
  its 
  composure, 
  when 
  it 
  renews 
  the 
  attack, 
  persever- 
  

   ing 
  until 
  the 
  helpless 
  victim 
  succumbs 
  to 
  repeated 
  wounds 
  and 
  is 
  

   finally 
  devoured. 
  The 
  second 
  caterpillar 
  of 
  the 
  series 
  is 
  then 
  at- 
  

   tacked 
  in 
  the 
  same 
  way, 
  and 
  so 
  on 
  with 
  each 
  in 
  turn, 
  until 
  the 
  larval 
  

   wasp 
  gains 
  a 
  size 
  and 
  strength 
  that 
  enables 
  it 
  to 
  abandon 
  its 
  sus- 
  

   pended 
  cable 
  and 
  make 
  its 
  attack 
  on 
  foot. 
  The 
  quantity 
  of 
  food 
  

   originally 
  stored 
  for 
  it 
  is 
  nicely 
  regulated 
  to 
  its 
  needs, 
  being 
  neither 
  

   too 
  much 
  nor 
  too 
  little 
  for 
  its 
  growth 
  and 
  development. 
  When 
  ten 
  

   or 
  twelve 
  days 
  old 
  it 
  is 
  prepared 
  for 
  its 
  change 
  to 
  the 
  pupa 
  state, 
  in 
  

   which 
  condition 
  it 
  remains 
  encysted 
  within 
  its 
  cell 
  for 
  several 
  months. 
  

   At 
  the 
  end 
  of 
  this 
  pupal 
  period 
  it 
  transforms, 
  of 
  course, 
  to 
  the 
  adult, 
  

   gnaws 
  its 
  way 
  out 
  of 
  the 
  cell, 
  and 
  escapes. 
  

  

  The 
  prevention 
  of 
  this 
  interference 
  with 
  the 
  air 
  brake 
  b)^ 
  solitary 
  

   wasps 
  would 
  seem 
  to 
  be 
  a 
  matter 
  of 
  no 
  great 
  difficulty. 
  Commenting 
  

   upon 
  my 
  suggestion 
  that 
  access 
  to 
  the 
  interior 
  of 
  the 
  valve 
  be 
  prevented 
  

   by 
  making 
  the 
  passageway 
  with 
  an 
  angular 
  or 
  spiral 
  turn, 
  or 
  by 
  

   making 
  the 
  air 
  opening 
  in 
  the 
  form 
  of 
  a 
  narrow 
  slit 
  instead 
  of 
  a 
  

   circle. 
  Superintendent 
  Rhodes 
  says: 
  "The 
  best 
  suggestion 
  has 
  come 
  

   from 
  Mr. 
  Forbes, 
  and 
  is 
  contained 
  in 
  his 
  letter 
  of 
  October 
  26th. 
  An 
  

   angular 
  opening 
  or 
  one 
  with 
  slits 
  like 
  a 
  grating 
  would 
  be 
  quite 
  prac- 
  

   ticable. 
  We 
  trust 
  the 
  suggestion 
  will 
  be 
  immediately 
  acted 
  on 
  by 
  all 
  

   manufacturers 
  of 
  retaining 
  valves 
  for 
  air-brake 
  purposes. 
  One 
  other 
  

   change 
  in 
  application 
  should 
  be 
  observed. 
  Owing^to 
  the 
  construc- 
  

   tion 
  of 
  the 
  retaining 
  valves, 
  as 
  made 
  up 
  to 
  the 
  present 
  time, 
  the 
  open- 
  

   ing 
  must 
  necessarily 
  be 
  placed 
  facing 
  the 
  side 
  of 
  the 
  car. 
  This 
  adds 
  

   to 
  the 
  difficulty 
  of 
  cleaning 
  out 
  the 
  obstruction, 
  even 
  should 
  the 
  

   stoppage 
  be 
  discovered. 
  There 
  is 
  no 
  reason 
  why 
  this 
  should 
  not 
  be 
  

   placed 
  so 
  that 
  it 
  can 
  be 
  opened 
  up 
  with 
  a 
  wire 
  or 
  some 
  other 
  sharp- 
  

   pointed 
  instrument. 
  With 
  these 
  remedies 
  generally 
  known 
  and 
  ap- 
  

   plied, 
  it 
  is 
  believed 
  future 
  encounters 
  with 
  our 
  new 
  enemy 
  will 
  result 
  

   in 
  signal 
  victories 
  for 
  the 
  air 
  brake." 
  

  

  