﻿AIR-SACS 
  OF 
  THE 
  LOCUST. 
  183 
  

  

  respiratory 
  efforts 
  of 
  the 
  insect 
  in 
  effecting 
  its 
  change, 
  and 
  which, 
  with 
  a 
  tendency 
  to 
  

   enlarge 
  by 
  the 
  natural 
  forces 
  of 
  growth 
  in 
  these 
  structures, 
  results 
  in 
  the 
  dilatation 
  

   first 
  of 
  the 
  trachea? 
  at 
  the 
  base 
  of 
  the 
  abdomen 
  into 
  distinct 
  sacs. 
  This 
  is 
  the 
  man- 
  

   ner 
  in 
  which 
  the 
  air-sacs 
  are 
  formed 
  in 
  all 
  insects. 
  After 
  the 
  main 
  trunks 
  have 
  be- 
  

   come 
  dilated 
  their 
  ramifications 
  also 
  are 
  enlarged 
  in 
  like 
  manner, 
  and 
  this 
  enlarge- 
  

   ment 
  continues 
  from 
  the 
  time 
  when 
  the 
  insect 
  enters 
  its 
  pupa 
  to 
  that 
  of 
  its 
  appear- 
  

   ance 
  in 
  the 
  perfect 
  state. 
  

  

  There 
  is 
  no 
  more 
  admirable 
  instance 
  in 
  nature 
  of 
  the 
  adaptation 
  of 
  

   organs 
  to 
  the 
  performance 
  of 
  certain 
  functions 
  than 
  this 
  of 
  the 
  air-sacs, 
  

   which 
  render 
  certain 
  insects 
  true 
  aeronauts. 
  This 
  delicate 
  correlation 
  of 
  

   these 
  organs 
  to 
  the 
  aerial 
  habits 
  of 
  the 
  insects 
  which 
  possess 
  them, 
  seems 
  

   to 
  be 
  in 
  the 
  relation 
  of 
  cause 
  to 
  effect. 
  It 
  has 
  been 
  seen 
  that 
  they 
  do 
  

   not 
  arise 
  until 
  the 
  final 
  winged 
  state 
  of 
  the 
  insect 
  — 
  the 
  time 
  when 
  they 
  

   are 
  first 
  brought 
  into 
  use 
  — 
  and 
  this 
  is 
  an 
  indication 
  that 
  they 
  are 
  the 
  

   result 
  of 
  forces 
  acting 
  upon 
  the 
  organism 
  during 
  its 
  adult 
  winged 
  life. 
  

   This 
  special 
  adaptation 
  of 
  the 
  air-tubes 
  to 
  the 
  exigencies 
  of 
  its 
  aerial 
  

   life 
  may 
  have 
  been 
  suddenly 
  induced, 
  the 
  tracheae 
  in 
  some 
  favored 
  race 
  

   of 
  bee, 
  moth, 
  or 
  locust 
  having 
  been 
  distended 
  during 
  the 
  rapid, 
  violent 
  

   respiratory 
  efforts 
  of 
  the 
  insect 
  during 
  flight, 
  and 
  resulted 
  in 
  a 
  perma- 
  

   nent 
  enlargement 
  of 
  the 
  air-tubes. 
  These 
  initiatory 
  sacs 
  being 
  found 
  

   useful 
  were 
  probably 
  transmitted 
  to 
  the 
  offspring, 
  until 
  they 
  became 
  

   permanent 
  improvements 
  in 
  the 
  organization 
  of 
  certain 
  races 
  of 
  differ- 
  

   ent 
  groups 
  of 
  flying 
  insects, 
  and 
  remained 
  wanting 
  in 
  other 
  even 
  closely 
  

   allied 
  groups 
  which 
  did 
  not 
  possess 
  wings. 
  Thus 
  we 
  see 
  that 
  changes 
  

   in 
  the 
  mode 
  of 
  life, 
  the 
  influence 
  of 
  the 
  environment 
  upon 
  the 
  insect, 
  pro- 
  

   voked 
  the 
  variation, 
  i. 
  e., 
  the 
  sudden 
  rise 
  of 
  what 
  ultimately 
  proved 
  to 
  be 
  

   useful 
  organs 
  which 
  became 
  further 
  perfected 
  and 
  finally 
  absolutely 
  in- 
  

   dispensable 
  and 
  unfailingly 
  present 
  in 
  the 
  descendants 
  of 
  those 
  forms 
  

   in 
  which 
  they 
  at 
  first 
  originated. 
  Such 
  is 
  the 
  line 
  of 
  thought 
  or 
  argu- 
  

   ment 
  which 
  we 
  are 
  compelled 
  to 
  adopt 
  in 
  endeavoring 
  to 
  trace 
  the 
  origin 
  

   of 
  such 
  organs 
  as 
  those 
  under 
  consideration. 
  In 
  brief, 
  it 
  is 
  the 
  influence 
  

   of 
  external 
  causes 
  upon 
  the 
  animal, 
  certain 
  changes 
  in 
  the 
  environment, 
  

   which 
  become 
  perpetuated 
  by 
  internal 
  causes 
  or 
  inheritance 
  force. 
  

  

  CHAPTER 
  X. 
  

  

  HISTOLOGY 
  OF 
  THE 
  LOCUST 
  (CALOPTENUS) 
  AND 
  THE 
  

   CRICKET 
  (ANABRUS). 
  (Plates 
  II-VIII.) 
  

  

  By 
  Dr. 
  Charles 
  Sedgwick 
  Minot. 
  

  

  Insects 
  have 
  hitherto 
  been 
  but 
  little 
  studied 
  by 
  histologists. 
  The 
  

   science 
  of 
  general 
  anatomy 
  or 
  histology, 
  which 
  was 
  first 
  established 
  by 
  

   Bichat 
  in 
  France, 
  acquired 
  a 
  fresh 
  importance 
  and 
  new 
  meaning 
  through 
  

   the 
  investigations 
  of 
  German 
  naturalists, 
  and 
  above 
  all 
  through 
  the 
  

   great 
  discovery 
  of 
  Schwann 
  that 
  all 
  animals 
  are 
  composed, 
  like 
  plants, 
  

   of 
  certain 
  minute 
  elements 
  or 
  units, 
  which 
  are 
  now 
  familiar 
  to 
  all 
  natu- 
  

  

  