1>11EFACE 



Here are a few chips left over from the authors' workshop. 



First of all we do not pretend to ha\'e presented herein the last 

 word in a field already overcrowded by worthy ri\'als. The "last 

 word" has an undesirable mortuary connotation quite out of keeping 

 in a book about living things. 



The authors have been teaching biology for a total of ninety-four 

 academic years, in addition to over sixty seasons of strenuous service 

 in summer field work with classes at marine and fresh-water labora- 

 tories, and they can truthfully and enthusiastically say that they 

 have enjoyed this experience. 



If what they would pass on to other students of biology appears 

 from the table of contents to bear the familiar marks of old stuff, the 

 reason is that it represents, in their minds at least, what remains 

 after many years of trial and elimination at the hands of an army of 

 different teachers and scholars. The fact that much material that has 

 been worked over before it was retained does not necessarily prevent, 

 it is hoped, some degree of freshness in its presentation. Any text- 

 book, the authors hold, should be somewhat like a dish of uncracked 

 nuts, accompanied by a good substantial nutcracker. It is desirable 

 that the reader should have some of the fun of wielding the nutcracker, 

 for no pedagogical cellophane can preserve nuts already shelled in an 

 entirely fresh and satisfactory condition for a very long time. 



An inevitable handicap that the textbook method of presentation 

 of any subject is bound to suffer, is the fact that between the covers 

 of a book the whole banquet is set upon the table at once in a more or 

 less complete array. It is the part of the instructor to break up the 

 feast into courses and to serve them in digestible portions. Perhaps 

 the method of suspense employed in magazine serials woidd furnish a 

 better way of arriving at the desired end than presenting the matter 

 all at once in l^ook form, since sufficient time shoukl always be pro- 

 vided between the planting and harvesting of intellectual ideas to 

 allow for unforced sprouting and growth. 



In the use of any textbook it is well to remember that the pages 

 may be turned backward as well as forward, and that it is no crime 

 either to skip or to reread. 



Every studious and effective reader, moreover, is wary about 



