The numerous data in the International Whaling Statistics relating foetal length to date of catch have been studied. They can be used as alternatives to cube roots of foetal weights to give rates of foetal growth and for the computation of data of conception and foetal ages. There are major differences between the Mysticeti and Odontoceti. The main gestation period for the former is 10.8.±1‐2 months and for the latter 14 ± 2 months. In both groups the greatest birth‐weight is attained by an increased foetal growth rate, to such an extent in the rorquals that the gestation period in the largest is actually shorter than in the smaller species. There are dietetic and metabolic differences between the two sub‐cohorts. The outstanding one is that pregnant mysticetes appear to stop feeding and lose body fat to the foetus during late pregnancy, at the time when the foetal increase in size is maximal. The causes of the differences in growth and metabolism of the two groups are unknown, apart from those imposed by differences in their ecology.

While the larger cetaceans have the greatest known specific foetal growth rates (Huggett & Widdas, 1951), examination has shown that among land mammals of a particular Order, Sub‐order or even Genus, there may be marked variation in rates.

Breeding site characteristics have been studied for the three species of newt that occur in Britain, the Palmate (Triturus helveticus (Razoumowski)), Smooth (T. vulgaris (L.)) and Warty (T. cristatus (Laurenti)). The Warty newt was seldom found in the absence of the much commoner Smooth newt, but seemed to prefer sites that were relatively large and deep and that had a high proportion of open water surface. All three species tended to breed in ponds having abundant aquatic vegetation. Smooth newts, unlike Palmate newts, were rarely encountered in water with pH <6. The Smooth newt tended to be found in water with relatively high concentrations of metals, while the reverse was true for the Palmate newt. Over Britain, Smooth and Warty newts are relatively less common in soft water areas, while the Palmate is less common in hard water areas. Possible reasons for these associations are discussed.

SUMMARY1. Diminishing the food supply to pregnant rats was associated with a subnormal degree of foetal loss among the larger litters, but a greatly lowered intake increased this foetal loss.2. Whether the food intake was lowered, normal or increased, the increase in conceptus weight over the last half of pregnancy could be related to the total maternal weight increase over this period by the formula y = ix + 4-5n, where n was the number of foetuses.3. With values of x below 20 g, this no longer held, but y never fell below 4.5 (n + 1).4. It is concluded that Hammond's theory of the partition of nutrients is confirmed, so far as mother and conceptuses are concerned, in the rat.

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