534 ON THE FEET OF CERTAIN MAMMALS. [June 20, 



tissue, they are, I believe, elastic, and must be considered a modi- 

 fied 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 re- 

 spectively 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 LV. 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 integumentary layers 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 

 evidentlv are used to assist the foothold when climbing. In no other 

 species have I observed similar projections ; and this is another pecu- 

 liarity in which this remarkable species differs from all other Bats. 



In Mystacina tubercuhtta (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 re- 

 markable 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 spe- 

 cially 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}. Un- 

 doubtedly 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 in clinging to smooth surfaces where the claws are 

 unable to penetrate sufficiently deep. 



EXPLANATION OF PLATE LV. 



Fig. 1. Foot of Vespentgo nanus, Ptrs. 



1 a, 4«. Thumb of ditto. 



2. Foot of V. pacliyims, Temm. 



2 a, 5 a. Thumb of ditto. 



3. Foot of V. tylopvs, Dobson. 



