Fig. 72 is a sketch of the hand and foot of a squirrel (Sciurus) and the numbers 1, 2, 3, 4, 5 and 6 are placed conspicuously on the walking pads in accordance with the teaching of Dr. and Mrs. Wilder Harris as to the six palmar and plantar walking-pads, of which the typical palm and sole is constructed. The thick, black lines indicate the flexures formed round the pads by the exercise of the functions of the hand and foot. Fig. 73 represents the clumsy, thick walking-pads of a marsupial the vulpine phalanger, _trichosurus vulpecula_. Fig. 74, the highly-developed prehensile foot of the loris. Fig. 75, the foot of a ring-tailed lemur. Fig. 76, the foot of a squirrel-monkey (Chrysothrix Sciurea). Fig. 77, the foot of a macacus (Macacus cynomologus). Fig. 78, the foot of a gibbon. Fig. 79, the hand of a chimpanzee and here the resemblance to the _hand_ of man and _not to the foot of man_ is very striking. A description has already been given of man’s flexures of the palm. [Illustration: Fig. 80.--Drawing of flexures of sole of foot in young adult.] Fig. 80 is a careful drawing of the sole of a young active woman with a well-formed foot, and there is little typical in the mode of arrangement of its creases except the slight tendency to transverse lines of flexure. In all the feet I have examined I have found no single flexure that is constant, and the longitudinal ones here shown are often absent. Reviewing these examples one observes an evolutional decay of a minor but necessary piece of mechanism of the Primate hand and foot. The general similarity, _mutatis mutandis_, of the flexures of the palm and sole in Primates is very noticeable, and is associated with the strong prehensile power of the foot of all the forms below man. In the cases of the two apes shown in this series, the resemblance is still well marked, more so even in the chimpanzee than the gibbon, so that the disappearance from the sole of man’s foot of any important flexure is very significant of his loss of prehensile and gain of locomotive perfection, and I find it impossible to conceive any process of evolutionary change where a loss of the flexures of a prehensile foot could come under the power of selection, on its own merits. On the other hand this remarkable instance of disuse of a formerly useful structure is adequately accounted for by the evolution of an organ like the human foot which in course of long periods of time became an organ of one function. Weismann might score a point over Spencer from his laboured explanations of man’s dwindling little toe, but here, I submit, he would have had to take refuge in silence, and pass to characters of a higher and more debateable kind. CHAPTER XX. THE EVOLUTION OF A BURSA.