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Show /J34 ON THE FEET OF CERTAIN MAMMALS. [June 20, tissue, they are, I believe, elastic, and must be considered a modified condition of the corium of the sole of the foot, their form being dependent on the direction in which the stretching force acts when the edge of the disk is fixed. The circular rim of the suctorial disk is composed of the free margins of the outer and inner layers of integument (homologous respectively with the integument covering the sides and soles of the foot in other Bats) which together form a flattened elastic ring (as shown in Plate L V . fig. 5), which, moistened by the secretions of the sudorific glands opening on the concave surface of the disk, fits accurately to any smooth surface on which it may be placed. The simple action of throwing the weight of the body on the base of the cup while its circular rim is applied to any smooth surface, is sufficient to fix it there : for the integumentarv lavers and connective tissues of which it is composed are thereby stretched, and its concavity increased in depth, thus causing a partial vacuum. That these suctorial disks are not always sufficient alone to enable the animal to climb is shown by the presence of small projections from the posterior margin of the calcaneum (Plate LV. fig. 6), which evidently are used to assist the foothold when climbing. In no other species have I observed similar projections ; and this is another peculiarity in which this remarkable species differs from all other Bats. In Mystacina tuberculata (of which several peculiarities have been described by me in a preceding paper, see above, p. 486) the sole of the foot is formed of deeply wrinkled very lax skin, which also extends along the inferior surface of the flattened and short legs (Plate LV. fig. 7). The toes, in the arrangement of the integument, present a remarkable resemblance to those of Hemidactylus (comp. fig. 8). Each toe is divided by a central groove, from which smaller transverse grooves proceed outwards to the margins. As I have shown (in the paper referred to), the whole external structure of this species is peculiar: the wings and interfemoral membrane are folded away beneath a portion of the membrane along the sides of the body, which is specially thickened, and forms a protective case as perfect as the elytra of a coleopterous insect, with which it is, indeed, strictly analogous ; the extremities are very strong, and the claws armed with basal denticles (Plate LV. fig. 7 a), so that this species is the most quadrupedal of Bats, and also the most fitted for climbing among all the known species of Chiroptera (except perhaps Thyroptera tricolor). Undoubtedly the sole of the foot and under surface of the leg are specially modified in relation to the habits of the animal, assisting it most materially iu clinging to smooth surfaces where the claws are unable to penetrate sufficiently deep. EXPLANATION OF PLATE LV. Fig. 1. Foot of Vesperugo nanus, Ptrs. I a, 4 a. Thumb of ditto. 2. Foot of V. pachypus, Temm. 2 a, 5 a. Thumb of ditto. 3. Foot of V. tylopus, Dobson. |