We made a survey on the degree of difficulty of the contents in biology textbook for high school students. Six hundred three students who completed the course of Science(I) participated in this study. The survey disclosed that the most difficult part was `Life Continuity` (58.0%). Of these students 26.6% replied that the most difficult chapter in that part was `Development`, marking second highest point next to `Genetics`. `Induction` and `Cell Differentiation` were the most difficult section in `Development` chapter. To investigate. how senior high school students think of studying embryology in the part of `Life Continuity`, we asked some questions. The degree of difficulty in studying embryology was 3.71/5 (S.D.=75) and the degree of indifference was 4.13/5 (S.D.=0.87), indicating that embryology was a difficult and disinterested course for student to learn it. But there was no difference to the degree of difficulty and indifference with sex. High school text books (10 kinds), and manuals of experiments for general biology (6 kinds), and developmental biology (8 kinds) for college students were also analysed for this study. Experiments for learning animal development in high school and in college employed only contents to observe the developmental process in morphological aspect. Although the contents of experiments for developmental biology manuals were more or less various, it was concluded that they were not well organized because of lacking the sequential arrangement.