82 INITIATIVE IN EVOLUTION 



the conclusion reached in Chapter I. that muscular action can 

 change the direction of hair in the individual. If at the same time 

 the degree and extent of the jolt which occurs here at every step 

 be noted, it is seen to be sharply limited to the area covered by 

 this pattern, and ceasing, as it does, abruptly and significantly at 

 the level of the iliac crest. The forward range of the jolt, easily 

 seen in a thin horse, is much wider than the backward, and marks 

 out very closely the extent of the forward curve taken by the 

 anterior hair-stream as it descends from the crest. One may also 

 remark that there is a small but interesting point which one can 

 see during or after a shower of rain, for then the flank of a horse 

 presents a curious distribution of the moisture. At the very point 

 where the forward stream joins the main stream from the thorax 

 and abdomen a definite line of darker moist hair is to be seen and 

 the moist-looking surface is limited to the stream of the trunk and 

 separated from that of the flank. This line of demarcation clearly 

 indicates the place where the forward jolt terminates during rapid 

 movement. 



The Domestic Ass and Mule. 



There are two closely related animals, the domestic ass and 

 the mule, which ought to show this inguinal pattern if affinity and 

 variation could be fairly invoked to account for it on the theory 

 of selection. These are also animals whose mode of life is loco- 

 motive, but in a much less degree than the horse and their paces 

 are quieter and less free in character. What then is found in them 

 as to the size or persistence of this pattern ? In the ass it is absent 

 or nearly so (I have found one example of its presence), and in the 

 mule it is variable and never occupies more than half the area of 

 that in the horse. These facts agree closely with the hybrid 

 character of the mule and the differing activities of the horse, mule 

 and ass. The pattern in Przewalski's horse is small and oval and 

 resembles that of the mule. The onager (equus asinus), which 

 is very much like these three domestic animals in form, has an 

 inguinal pattern, much less in size indeed than that of the horse, 

 but well-defined, and this fact is in keeping with its character for 

 remarkable fleetness of foot and activity. The three zebras, 

 Mountain, Grevy's and Burchell's, show no inguinal pattern, in 

 spite of their power of rapid locomotion and resemblance in size 

 and form to the horse. Though they have that power they exercise 

 it in their wild lives for their own sakes alone, in the intermittent 

 way which is bound up with their habit of life, and not for the sake 

 of man, as in the case of the horse. 



