﻿400 
  AIJNUAL 
  EEPORT 
  SMITHSOKIAN 
  INSTITUTION, 
  lQ2l 
  

  

  enabled 
  to 
  maintain 
  their 
  balance 
  at 
  all 
  times 
  and 
  the 
  proper 
  posi- 
  

   tions 
  for 
  swimming, 
  running, 
  and 
  flying. 
  

  

  The 
  organ 
  that 
  enables 
  us 
  to 
  orient 
  ourselves 
  to 
  the 
  direction 
  of 
  

   gravity 
  is 
  not, 
  strictly 
  speaking, 
  a 
  sense 
  organ 
  of 
  gravity, 
  for 
  it 
  gives 
  

   us 
  no 
  sensation 
  corresponding 
  with 
  the 
  stimulus. 
  It 
  is 
  possible, 
  then, 
  

   that 
  in 
  our 
  reactions 
  to 
  gravity 
  we 
  ourselves 
  experience 
  something 
  

   of 
  the 
  nature 
  of 
  an 
  automatic 
  tropism. 
  Though 
  we 
  are 
  conscious 
  

   of 
  the 
  muscle 
  tensions 
  which 
  keep 
  our 
  heads 
  upward, 
  and 
  of 
  the 
  

   pressure 
  of 
  our 
  bodies 
  on 
  other 
  surfaces, 
  we 
  have 
  no 
  actual 
  gravity 
  

   sensation 
  analogous 
  to 
  the 
  sensation 
  of 
  sight, 
  sound, 
  etc., 
  and 
  we 
  

   certainly 
  should 
  never 
  refer 
  our 
  faculty 
  of 
  equilibrium 
  to 
  the 
  region 
  

   of 
  the 
  inner 
  ear 
  if 
  we 
  had 
  never 
  studied 
  physiology, 
  

  

  REACTION 
  TO 
  LIGHT 
  ( 
  PHOTOTROPISM 
  ) 
  

  

  The 
  multitude 
  of 
  insects 
  seen 
  swarming 
  about 
  street 
  lamps 
  on 
  warm 
  

   summer 
  nights 
  is 
  proof 
  sufficient 
  that 
  many 
  species 
  are 
  strongly 
  

   affected 
  by 
  light 
  and 
  go 
  toward 
  its 
  source. 
  The 
  observation, 
  of 
  

   course, 
  for 
  reasons 
  already 
  given, 
  does 
  not 
  prove 
  that 
  insects 
  see 
  

   light 
  as 
  we 
  see 
  it, 
  or 
  that 
  nocturnal 
  species 
  seek 
  the 
  light 
  because 
  

   they 
  find 
  night 
  life 
  agreeable 
  in 
  its 
  presence. 
  For 
  the 
  most 
  part 
  

   insects 
  found 
  about 
  lights 
  are 
  species 
  that 
  do 
  not 
  fly 
  in 
  the 
  day- 
  

   time; 
  they 
  are 
  species 
  that 
  are 
  attuned 
  to 
  dim 
  lights. 
  But, 
  as 
  Ken- 
  

   nedy 
  has 
  interestingly 
  pointed 
  out, 
  most 
  insects 
  must 
  be 
  hypersen- 
  

   sitive 
  to 
  light 
  on 
  account 
  of 
  the 
  relatively 
  great 
  size 
  of 
  their 
  com- 
  

   pound 
  eyes. 
  Compound 
  eyes 
  have 
  to 
  be 
  large 
  in 
  order 
  to 
  be 
  at 
  all 
  

   efficient 
  as 
  organs 
  of 
  vision. 
  As 
  a 
  consequence 
  the 
  insect 
  is 
  over- 
  

   stimulated 
  in 
  the 
  presence 
  of 
  unusually 
  strong 
  illumination, 
  and 
  

   nocturnal 
  species 
  swarm 
  to 
  bright 
  lights 
  if 
  the 
  nervous 
  organization 
  

   for 
  making 
  light 
  responses 
  is 
  not 
  provided 
  with 
  a 
  controlling 
  or 
  

   inhibiting 
  mechanism, 
  which 
  night-flying 
  insects 
  would 
  not 
  need 
  

   under 
  natural 
  conditions. 
  On 
  coming 
  into 
  the 
  immediate 
  neighbor- 
  

   hood 
  of 
  the 
  light, 
  however, 
  some 
  insects, 
  Kennedy 
  observes, 
  are 
  

   rendered 
  inactive 
  by 
  the 
  excessive 
  degree 
  of 
  stimulation 
  here 
  encoun- 
  

   tered 
  and 
  sit 
  motionless 
  in 
  the 
  full 
  glare. 
  

  

  Insects 
  that 
  react 
  definitely 
  to 
  light 
  are 
  either 
  positive 
  or 
  negative 
  

   in 
  their 
  responses. 
  Flies 
  will 
  leave 
  a 
  darkened 
  room, 
  roaches 
  will 
  

   go 
  into 
  it. 
  Not 
  many 
  species, 
  however, 
  are 
  attracted 
  by 
  total 
  dark- 
  

   ness, 
  and 
  a 
  so-called 
  negative 
  reaction 
  to 
  light 
  is 
  in 
  most 
  cases 
  a 
  

   positive 
  reaction 
  to 
  a 
  low 
  degree 
  of 
  light. 
  In 
  experiments 
  it 
  is 
  often 
  

   found 
  that 
  an 
  insect 
  is 
  attracted 
  by 
  light 
  up 
  to 
  a 
  certain 
  intensity, 
  

   but 
  is 
  repelled 
  if 
  the 
  intensity 
  is 
  increased. 
  Most 
  nocturnal 
  insects 
  

   are 
  photopositive, 
  as 
  is 
  shown 
  by 
  their 
  attraction 
  to 
  lights 
  at 
  night. 
  

   Many 
  of 
  them 
  also 
  exhibit 
  positive 
  light 
  reactions 
  if 
  they 
  are 
  dis- 
  

   turbed 
  during 
  the 
  day. 
  

  

  