INTRODUCTION. 



This Guide is a series of replies to questions which 

 have arisen in the minds of its authors while teaching. 

 Many of the answers appear in the unsatisfactory form 

 of quotations from various observers. These are often 

 contradictory, and for this reason sometimes confusing 

 to ordinary minds which demand certainty ; and to 

 teachers and scholars who are inclined to rely upon 

 definitions. In the sciences of observation, except 

 where experience has accumulated, certainty is un- 

 attainable and definitions often fuller of error than of 

 truth. 



Teacher and scholars should, recognize that science 

 is infinite, and demands from all its votaries a modest 

 acknowledgment of this fact. They should work more 

 as companions learning from each other's observa- 

 tions, and less as teacher and pupils, than in those 

 studies which can be taught from written treatises. 



The frequent reiteration of the statement, that a 

 person does not know a certain fact or series of facts 

 will cause no distrust in scholars who are trained to 

 study the things themselves, and are thus led to realize 

 the vast extent of the field of work in every organism. 



A teacher need not be discouraged because a library 

 is not accessible ; specimens of some kind, and gen- 

 erally of many kinds, can be obtained. These are 



