THE CRAYFISH: 
AN INTRODUCTION TO THE STUDY OF ZOOLOGY. 
CHAPTER I. 
THE NATURAL HISTORY OF THE COMMON CRAYFISII 
(Astacus fluviatilis.) 
Many persons seem to believe that what is termed 
Science is of a widely different nature from ordinary 
knowledge, and that the methods by which scientific 
truths are ascertained involve mental operations of a 
recondite and mysterious nature, comprehensible only by 
the initiated, and as distinct in their character as in 
their subject matter, from the processes by which we 
discriminate between fact and fancy in ordinary life. 
But any one who looks into the matter attentively will 
soon perceive that there is no solid foundation for the 
belief that the realm of science is thus shut off from that 
of common sense ; or that the mode of investigation which 
yields such wonderful results to the scientific inves- 
tigator, is different in kind from that which is employed 
B 
