1. Stevenson et al. (1966)
2. Emanuel et al. (1972)
3. The most obvious explanation of such a phenomenon is that some environmental factor causes predominantly female anencephalics, and that another factor affects the sexes almost equally. This latter factor might be genetic or environmental, but, to judge from Fig. 6 of Leck (1972), it seems to be rather evenly distributed across populations. The same Fig. suggests that the environmental factor only operates substantially within Caucasian populations. This presumably is the explanation of the general failure to find environmental variation of anencephaly rates (for example, by season and class) in those populations in which the incidence is low. It is not, I suggest, that low incidence populations can only provide small samples in which, for reasons of statistical power, such variation is not detectable, but that the variation does not exist to a comparable extent in those populations anyway
4. suggested that the sex ratio of anencephalics is dependent jointly on the incidence of anencephaly and the dizygotic twinning rate. In contrast, I have suggested;Knox,1974
5. At present, a woman may avoid a second neural tube defect by the process of amniocentesis and selective abortion, but the fact that defective fetuses can be identified is no reason for relaxing efforts to diminish their incidence. An abortion can never be regarded more favourably than as the lesser of two evils. It seems unlikely that the unfortunate wisdomafter-the-event that followed the potato trials (Lemire;(Knox,;et al; will indefinitely deter clinicians from further work in this field. So one may expect, and welcome the possibility, that clinical trials will sooner or later be initiated to test tea,1978