The skin over the trunk and limbs of man is exposed to stimuli of pressure, friction, heat, cold and wind in very different degrees, according to the part which it covers. I do not here refer to nocuous, or so-called noci-cipient stimuli, as being too casual in their incidence for the question in hand. Broadly the ventral surface of the neck and trunk differ much, in respect of the qualities of their epidermis, from the dorsal. The skin over the former is softer, thinner and more flexible than the latter, which is in adult life thick, hard and with larger openings of the sebaceous glands. As the two main layers of the skin are so closely united it is impossible to state any general rule as to the parts played in this manufacture by the epidermis and dermis respectively. Altogether the skin from the dorsal surfaces of mammals provides a much denser fabric than the latter, and different qualities of leather are obtained from different regions. Corresponding differences of texture are found on the extensor and flexor surfaces of the limbs, especially on the hands and feet. In the course of his long evolution from a hairy stock, whether simian as we thought yesterday, or a lower one as Professor Woods Jones suggests to-day, these dorsal surfaces of neck, trunk and extensor surfaces of limbs have been exposed through countless generations of men to vastly more stimuli of friction, pressure, and response, than those of the ventral and flexor regions. As man’s hairy covering diminished, through some mysterious and at present unrecognised cause, these stimuli became increasingly potent in producing a tissue denser than that of the more protected ventral parts where all forms of these stimuli are slight. I do not claim that this was a phenomenon that began with man, for in a measure it was present in those forms which preceded him, and in many related mammals under the cover of their hairy covering.