Xll PREFACE 
of life-histories. A successful teacher of zoology once 
declared that frogs were created for the express purpose 
of serving as the introductory type in the study of that 
science; as strong a claim may be made for the fern in 
botany/ 
Such concepts as alternation of generations, sexual vs. 
asexual reproduction, fertilization, heredity, adjustment 
to environment, life-cycle are nowhere more clearly illus- 
trated than in the fern; the essence of them all may be 
clearly comprehended by anyone who has carefully studied 
its life-history. And with what a rich equipment may the 
life-histories of all other forms, both higher and lower, be 
then undertaken! As Athene sprang full armed from the 
imperial head of Zeus, so, from a study of the fern, do all 
the essentials of alternation, sex, life-cycle, et cetera, leap 
clearly denned into the mind of the beginning student, 
there to remain throughout the course, illuminating all 
subsequent studies of life-histories. 
During tht past fifteen or twenty years it has been the 
general, if not universal, custom to study in the laboratory 
the same forms as those treated in the text. Part II of 
the present book has been planned with the idea of having, 
for the most part, different sets of forms discussed in the 
laboratory and the lecture room. This plan not only gives 
the pupil acquaintance with a wider range of types, but 
also tends to insure greater independence in the laboratory 
work. It has been tacitly assumed that, in connection 
with the use of this text, substantially the same classic 
types will be studied in the laboratory as have formed the 
basis of laboratory work for two decades. They are not 
only types for which material may be obtained with com- 
parative ease in quantity, but also forms which have been 
