Fig. 12.—"Wing" of bat (Pipistrelle).

Hu., humerus, or arm-bone; Ul., conjoined radius and ulna, a bone in the forearm; Po., pollex, answering to our thumb; ii., iii., iv., v., second, third, fourth, and fifth digits of the manus, or hand. The figures are placed near the metacarpals, or palm-bones. These are followed by the phalanges. Fe., femur or thigh-bone; Ti., tibia, the chief bone of the shank. The digits of the pes, or foot, are short and bear claws. Ca., calcar.

From the point of the fifth or last digit the leathery wing membrane sweeps back to the ankle. The bones of the hind limb are the femur, or thigh-bone, and the tibia (with a slender, imperfectly developed fibula). There are five toes, which bear long claws. From the ankle there runs backward a long, bony and gristly spur, which serves to support the membrane which stretches from the ankle to the tip (or near the tip) of the tail.

Thus the wing of the bat consists of a membrane stretched on the expanded or spread fingers of the hand, and sweeping from the point of the little finger to the ankle. Behind the ankle there is a membrane reaching to the tip of the tail. This forms a sort of net in which some bats, at any rate, as I have myself observed, can catch insects.

I have selected the wing of the bat to exemplify variation, (1) because the bones are readily measured even in dried specimens; (2) because they form the mutually related parts of a single organ; and (3) because they offer facilities for the comparison of variations, not only among the individuals of a single species, but also among several distinct species.

The method employed has been as follows: The several bones have been carefully measured in millimetres,[O] and all the bones tabulated for each species. Such tables of figures are here given in a condensed form for three species of bats.

Bat-Measurements (in Millimetres).
R&UPo2nd Digit.Third Digit.Fourth Digit.Fifth Digit.Tibia.
M.M.P1.P23.M.P1.P23.M.P1.P23.
Hairy-armed bat (Vesperugo leisleri).41 6.5 38 40 16 19 38 14 7 32 8 7 16♂
41 6 38 40 16 19 39 15.5 7 33 8 6.516♂
41 6 39 40 16 18 39 16 6.5 33 8 7 16♂
41.55 39 40.517 20 39 16 7 33 8 7 15♂
40 6 39 37 15.518 37 14.5 7 32 8 6.515♀
41 5.5 38.5 39 16.520 39 15 7.5 33 8 7.517♀
41 6 39 40 15.520.5 39 15.5 7 33 8 7 16♀
Horseshoe bat (Rhinolophus ferri-equinum).51 5 39 36 19 29 40 11 18 40 13 15 22♂
54 5 40 36 18 32 40 11 19 40 14 16 28♀
52 5 39 36 18 31 39 10 19 40 13 14 23♀
54 5 39 36 18 32 40 11 17 40 13 13 25♀
46 5 36 34 16 29 36 10 19 36 13 17 22?
Lesser horseshoe bat (Rhinolophus hipposideros).34 4 25 23 12 17 26 6.5 12 26 9 13 17♂
37 3 26 24 13 20 28 8 13 28 9 14 17♂
35 3 26 24.5 13 17 27 7 12 26 10 12 15♂

Transcriber's note: In the preceding table some headings have been shortened to save space. The key is as follows: