DEVELOPMENTAL BIOLOGY AND THE STUDY OF MALFORMATIONS

Summary 1. The scientific approach to malformations began with experimental work on abnormal conditions of incubation in the chick. 2. More precise experiments on causing abnormalities had a common origin with experimental embryology. 3. Progress in experimental teratology during the last fifty years is reviewed in a commentary on the four principles formulated by Stockard in 1921. 4. Some relationships are traced between the results of cytogenetical studies in man and in other organisms. 5. An account is given of present knowledge concerning malformations of the neural tube originating either experimentally, spontaneously, or phenotypically. 6. The teratological implications of some recent theories on the expression of the genotype are discussed, particularly in relation to problems of hormones as teratogens. 7. Some account is given of the implication of carbohydrate metabolism and terato‐genesis. 8. Teratogenesis is possibly related to cationic balance in early development. 9. It is suggested that one factor retarding progress in the understanding of malformations is the tendency towards the development of teratology in an insufficiently close relationship with other branches of cell biology.