96 MATERIALS FOR A MEMOIR ON 



seen that the giraffe uses the pace for all rates of movement; also 

 that the horse modifies his paces by the character of the ground 

 he traverses. It is probable in like manner that an animal will 

 by natural selection determine his methods of progression. Marsh- 

 dwellers are uniformly of the heavy-bodied, short-legged type. 

 In an animal emerging from the marsh to the plains the limbs 

 would become more compact and longer and the gait more various.* 

 Catonf states that the Virginia deer bounds up once or twice at 

 the beginning of his gait, to observe the surrounding country be- 

 fore he settles down to a steady run. This habit would be of no 

 use in an animal living on a prairie, and is absent in the mule- 

 deer. Mere speed is not a necessity of a change of gait. A trot 

 can be based on the walk; the fast pace on the slow pace. In the 

 opinion of Dr. M. H. Cryer, a horse in going over a hurdle em- 

 ploys the same division of his stride as in the run. 



Variability of gait in a single animal may be accepted as an 

 evidence of high development. Diversity of function in the 

 study of the gait is of the same value as in other subjects of 

 biology. Thus, an animal starting a movement on the laterals 

 by bringing into use a member of the opposite side, so that three 

 feet may be on the ground at the same time, can develop a walk 

 from the primitive pace, and can either maintain it at will or, 

 shifting from the right to the left lateral support, show a high 

 degree of division of functional labor in the use of the limb. In 

 like manner, when an animal wishing to increase his rate of speed 

 can by election leave the walk to amble, gallop, trot, or pace, an 

 advantage is secured over another animal in which the choice is 

 either withheld or limited. 



Of the two pairs of limbs, the front one is the more adaptive 

 for the reason that it is capable of so many secondary modifica- 

 tions, as grasping, flying, etc. We may assume by analogy that 

 the fore limbs are active in changing gaits, the hind limbs acting 

 in a more rigid and uncompromising manner. (See p. 51.) 



* According to F. C. Selous, Proc. Zool. See. London, 1881, p. 72G, Rhi- 

 noceros simus can gallop. 



f Antelope and Deer of North America, p. 270. 



