May  records  (Ent.  Recordy  vii.,  p.  238)  an  experiment  which
goes  to  show  that  after  pale  cocoons  are  spun  in  confinement,
exposure  to  damp  surroundings  tends  to  darken  them.  He  states
that  from  dark  cocoons  received  from  Yorkshire,  small  imagines
were  bred,  that,  from  a  pairing  of  these,  eggs  were  obtained  and
the  larvae  divided  into  two  lots:  (i)  Fed  on  abundant  supply  of
fresh  whitethorn,  in  roomy  cage,  dry,  light  and  well  ventilated ;
19  spun  up  producing  18  more  or  less  pale-coloured  and  only  one
dark  cocoon.  (2)  Fed  on  whitethorn,  often  short  of  food,  under  a
glass  shade  without  ventilation,  in  a  continuously  damp  atmosphere ;
16  cocoons  resulted,  every  one  dark.  On  November  24th  three  of  the
pale  cocoons  were  placed  on  damp  sand  in  the  forcing  cage,  kept  in  a
kitchen,  and  three  days  later  the  cocoons  were  noticed  to  be  dark
brown ;  wishing  to  make  sure  that  this  change  was  due  to  moisture
three  more  were  placed  with  them,  and  on  taking  them  out  two
hours  later  the  change  had  already  taken  place.  May  suggests
that  the  colour  of  the  cement  that  is  used  in  the  construction  of
the  cocoon  and  that  makes  it  waterproof,  is  perhaps  influenced
by  dampness  and  gives  the  cocoons  their  colour.  He  notes,  however,
that  the  cocoons  spun  by  his  larvae  were  thin  in  texture,  and  not
so  hard  as  those  he  had  had  before.  Reference  to  our  account  of
the  variation  of  the  cocoons  of  Lachneis  lanestris  {antecl^  vol.  ii.,  p.
512)  will  give  our  view  of  the  cause  of  the  variation  in  colour.
