1. The gross morphology, micro-anatomy, and histology of the blubber of the porpoise (Phocaena phocaena) and the rorquals (Balaenoptera spp.) are described.

2. If the surface area is given by Kl2, l being the overall length, then K is 0.39 in Phocaena and 0.35 in Balaenoptera, excluding fins and flukes.

3. Blubber consists of the whale's epidermis, dermis, and hypodermis. The hypodermis is relatively very thick and almost exclusively fatty, and in the species studied merges into the dermis which is mostly composed of white fibres. It extends into the epidermis as ‘dermal ridges’, from which the papillae arise. In the epidermis can be recognized: stratum germinativum, divided into the deep cylindrical cells and the more superficial prickle cells; and stratum corneum.

4. The vascular system is composed of arterioles running up to the base of the epidermis, giving rise to twigs which run up the dermal ridges to supply the capillaries in the papillae; and venules collecting twigs from the ridges and running down through dermis and hypodermis, connecting in the dermis with a venous plexus. Small ‘accompanying venules’ run with the arterioles to the base of the epidermis.

5. The conductivity of blubber is 0.00050 gm.-cal./sq. cm./°C./cm. and the deep body temperature is about 36° C. Thus in temperate and polar waters most whales lose heat at a greater rate than the basal metabolic rate of land homotherms, even when the blood-flow through the blubber is negligible. It is suggested that whales need to keep swimming in order to keep warm.

6. The vascular system in the blubber provides a mechanism for regulating heat loss.

7. It is shown that the energy liberated by the reduction in blubber thickness suffered by rorquals in the southern hemisphere during the winter is sufficient to meet at least a significant part of their total needs.

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