PREFACE. 
—_—. 
In writing this book about Crayfishes it has not 
been my intention to compose a zoological mono- 
graph on that group of animals. Such a work, to 
be worthy of the name, would require the devotion 
of years of patient study to a mass of materials 
collected from many parts of the world. Nor has 
it been my ambition to write a treatise upon 
our English crayfish, which should in any way pro- 
voke comparison with the memorable labours of 
Lyonet, Bojanus, or Strauss Durckheim, upon the 
willow caterpillar, the tortoise, and the cockchafer. 
What I have had in view is a much humbler, though 
perhaps, in the present state of science, not less use- 
ful object. I have desired, in fact, to show how 
the careful study of one of the commonest and most 
insignificant of animals, leads us, step by step, from 
every-day knowledge to the widest generalizations 
