There  are  striking  cases  on  record  which  warn  us
against  the  universal  correctness  of  the  view  that
the  environment  causes  an  adaptive  modification  of
the  organism.  Thus  the  writer  pointed  out  in  1889
that  positive  heliotropism  occurs  in  organisms  which
have  no  opportunity  to  make  use  of  it/  e.  g.,  Cuma
rathkii,  a  crustacean  living  in  the  mud,  and  the
caterpillars  of  the  willow  borer  living  under  the  bark
of  the  trees.  We  understand  today  why  this  should
be  so,  since  heliotropism  depends  upon  the  presence  of
photosensitive  substances,  and  it  can  readily  be  seen

*  Loeb,  J.,  Der  Heliotropismus  der  Tiere  und  seine  Uhereinstimmung
mit  dent  Heliotropismus  der  Pflanzen.  Wurzburg,  1890  (appeared  in
1889).
