1. The respiration rate of ova during their early cleavage stage from two groups of rats reared on diets of NDpCal% 10 or NDpCal% 5 has been measured, using a Cartesian diver.

2. Measurements from twenty-six experiments show that the average oxygen uptake of ova from the rats reared on the diet of high protein value was 0.563±0.175 mμl O2/ovum per h and the value for rats reared on the diet of low protein value was 0.440±0.076 mμl O2/ovum per h when measurements were made in a medium containing 0.9% NaCl and rat serum or plasma (2:1). The difference between these results was significant at 0.05 > P > 0.02.

3. It is suggested that the lower respiration rate of ova from rats maintained on the diet of low protein value may be due partly to the effect of dietary protein deficiency on conditions within the Fallopian tube and partly to the eRect on the maturation of the ovum itself.

1. Experiments on three pairs of male identical twin calves have shown that underfeeding at 2.5–6 months of age, i.e. during the critical stage of sexual maturation, considerably delayed the process of puberty, as regards testicular androgen production as well as secretion of fructose and citric acid by the seminal vesicles.

2. There was no marked difference in the blood-plasma content of non-protein nitrogen, vitamin A and carotene at 6 months, as between twins on a normal (N) and low (L) plane of nutrition, although the L-twins were growing and maturing more slowly. However, the blood-plasma content of glucose and of most of the free amino acids, was slightly reduced as a result of underfeeding.

3. When at the age of 6 months two twin-pairs were castrated and injected with either testosterone or androstenedione (50 mg every 3rd day, for 2 months), the L-twins of both pairs and the N-twin of one pair grew at a faster rate. Moreover, the concentration of nitrogen in blood plasma increased, the rise being particularly evident in the content of indispensable amino acids. This effect, however, was more pronounced in the N- than in the L-twins.

4. Testosterone treatment enhanced libido in the N-twin but not in the corresponding L-twin. Androstenedione had no effect on libido in either the N-twin or the L-twin. Thus, although testosterone and androstenedione both effectively promoted growth and nitrogen metabolism, androstenedione, unlike testosterone, was devoid of androgenic activity.