Evolution.

  • Society for Experimental Biology (Great Britain)
Date:
1953
Catalogue details

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Evolution. Source: Wellcome Collection.

    374/484 (page 342)
    344 LOCOMOTORY HABITS AND THE EVOLUTION employed, and the legs then execute larger angles of swing giving longer strides. Whether the legs of a pair are moved in the same or in opposite phase, or in some intermediate relationship, depends upon the pattern of the gait, and is controlled by functional needs. In 'bottom-gear' gaits, where there are POLYXENUS SCUTIGERELLA > Relative durations of forward and back strolces > 4-Ò:6-0 5-5:4-5 | | 2-5;7-5 3-3:7-7 5*2:4*8 Phase difference between successive legs a b Fig. 2. The movements of the legs on one side of the body oiPolyxenus and of the symphylan Scutigerella. Heavy Hnes denote legs in the propulsive backward stroke, and thin lines denote legs in the recovery forward swing. The slower gaits of each animal are shown on the left and the faster gaits on the right. The diagrams below show the disposition of the legs at the moment indicated by the vertical dotted line. In Fig. a the paired legs are in the same phase, and in Fig. b their phase difference is about 0-4, and in slightly faster gaits the phase difference becomes 0-5. Black spots mark the footprints, and their distance apart indicates the stride length. many propulsive legs at one moment, the paired legs are in the same phase. In 'top-gear' gaits, where few legs are propulsive at one moment, the legs are in opposite phase, and in 'middle-gear' gaits there is no functional advantage in either relationship, and animals other than Peripatus and Polyxenus employ either one or the other type of relationship but not both. Where the total number of legs is only three or four pairs, the phase