It has always seemed to me that the many parts that make up the subject of biology are related to each other more like the nodes of a web than as a linear collection of independent topics. So I believe that the power of hypertext will be better suited to learning about biology than is the linear structure of a printed textbook. Another disadvantage of printed textbooks is the inevitable delay between the time that new advances in biology are reported and the time that they can become incorporated in a printed book (often several years). Material here can be updated promptly. So although some of this information has been drawn from the sixth edition of the author's text Biology published in 1994 by Wm. C. Brown, every effort has been made to adapt the material to the opportunities provided by an online text.