For a number of years the first author has devoted much of his time to

the teaching of general college zoology, the second author to teaching ele-

mentary and advanced physiology, and the third author to teaching general

college biology. In addition, the third author has been closely associated with

the Biological Sciences Curriculum Studies (BSCS) and the Education Sec-

tion of the American Association for the Advancement of Science.

During this time we have seen changes in both the student body and

the philosophy of teaching in the field of biology. Many students come to

college now with a better background in scienee and mathematics than was

the case a decade past; yet not all do, for there are some secondary schools,

large and small, that have not kept pae~ and students from these schools have

not been given the advantages of up-to-date instruction. To avoid boring the

former while instructing the latter constitutes one of the major problems of

modern educators. We make no claim to having the solution, but we have

tried to keep the problem in mind while writing this book. As a consequence

it contains what we believe to be the bare essentials of scientific background

-in some cases oversimplified for clarity-but, at the same time, it incorpo-

rates more advanced concepts which we hope will challenge the able student

as well as the student with a strong academic background.