Abstract
A total of 1633 Wistar rat fetuses was used to determine weights of the fetus and several fetal organs on days 17 to 21 of gestation. Heart, lung, liver, kidney, stomach, intestine, brain, femur, thyroid and adrenal weights were recorded. Growth curves of the whole body and organs were calculated. A linear semi-log relationship between organ weight and day of gestation was shown. The doubling weight times were 1·5 days for whole bodies and for organs they ranged between 0·9 (spleen) and 3·4 (adrenals) days. A correlation between the rate of organ growth and the start of the organ function was observed.