Embryology of Behavior

normal as distinguished from abnormal young men. The problems encountered in deciding upon the criteria for normality and the selection of normal individuals for study are clearly set forth; the methods of scoring and the reasons for their selection are described and the selected data presented in the appendix include morphological, psychiatric, socioeconomic , and physiological records. These data are presented without interpretation, hence they will interest a very limited audience, but they will be of value to investigators or others prepared to speculate on their significance, and a careful reading of the book will save from many pitfalls others planning similar studies. 1945, pp. 289. $5. This book is a fascinating store of facts about the developing child from embryo to two years after birth. There is also much philosophical discussion about the fundamental directives and drives that lead to growth, integration, and individuation. Chapters I to VI take the reader through the first 28 weeks of fetal life from zygote to fetal-infant. Here are found the very beginnings of behavior. The first definite action is a twitch of the growing heart muscle which then begins to beat in the third week. The first movements of head and trunk occur when the embryo is about 8¼Y2 weeks of age. The mother may feel movements as "quickening" as early as the sixteenth week, but from the twelfth week on there are quite definite movements of the small muscles of face and eyeballs. In the descriptions of motor behavior emphasis is on the mechanisms of posture and respiration which are rudimentary in the embryo, but become important in the "fetal-infant," the name given to the child in the 28th to 40th weeks. In this period he might live if born, because the all-important mechanism of respiration is sufficiently developed at 28 weeks to make living possible outside the uterus. In the early part of this period the mechanism is poorly integrated and may not be able to sustain life for long, "survival hinges chiefly on the vitality of the basic neural mechanism." Respiration behavior is discussed at length in Chapter VII, with a good summary of Bar-croft's work on the sheep embryo. Chapter VIII takes up "muscle tonus," defined as "a continuous type of reflex which produces maintenance of posture ." Fetal behavior is said to be "largely progressive organization of the tonus of the skeletal muscular system." Chapter IX goes …