[The water impermeability of discontinuous animal integuments]

Discontinuous integuments formed by macroscopic discrete elements are characters mainly of land animals, both vertebrates and invertebrates. Waterproof properties of these integuments manifest themselves in capture and preservation of some air in their layers during submergence. The functions of integument air layer are various in different groups of animals, viz. participation in respiration (invertebrates with integuments in the form of plastron), insulation (especially birds and mammals), regulation of pelage state in the water (mammals). The principal condition of watertightness is high density of integument elements forming a system of capillaries with variable cross-sections. The general physical principle underlying the watertightness of integuments consist in a effect of surface tension arresting the water penetration deep into the coats soon as meniscus of a liquid has attend the widening section of intraintegumental capillary. For the watertightness of plastron formed by a single hair layer considerable stiffness of the whole system and high values of capillary pressure are important. Multilayered pliable mammalian pelage is characterized by a rather low capillary pressure because its effect is supplemented by the pressure that arise in the pelage air layer as a result of its compression during submergence. In birds with their structurally complicated integuments and diverse locomotory adaptations a wide spectrum of variability of plumage watertightness is observed.