KNOWLEDGE, 



[.Tanvary, 1903. 



kind of explanation." To tliese small and apparently 

 unimportant fraLfinents of nature's handiwork, wliich are 

 hei'e called pcilonu'tfrs for the sake of emphasis, this 

 unexceptionahle remark of the great logician applies. 



It may be best at the outset to state that, from their 

 intrinsic importance, whorls, featherings and crests are 

 excluded entirely from the province of any form of selec- 

 tion, being in no way useful to the animal possessing 

 them, and in no degree produced by artificial selection or 

 breeding. Their production must be sought elsewhere, 

 and no view of this is forthcoming but that which con- 

 siders them as by-products of muscular action in a long 

 line of ancestors, and in a very striking way they register 

 the degree and range of this action. 



As already stated, the best examples of the phenomena 

 in question, and the greatest number, are to be found on 

 the coat of the domestic horse, and these will first be 

 described. The best known is that graceful feathering 

 which passes upwards in the hollow of the tlank. dividing 

 the trunk of the animal from the great rounded mass of 

 muscle of the hind-quarters, and the feathering presents 



and the hinder one more directly in its original course along 

 the great swelling mass of the hind-quarters. A better idea 

 of the actual arrangements of the hair-streams will be 

 gathered from an inspection of the coat of any common 

 horse, whose coat is not too long, than can be conveyed 

 by a wiitten description. The symmetry and constancy of 

 this arrangement is very striking and demands explanation. 

 This is more fully treated in (1), (2), (3),* and it may ])e 

 shortly stated that these breaks in the uniform direction 

 of the hairy covering of the horse, and other animals, as 

 well as in other regions of their bodies than the inguinal, 

 are due to the constant traction, dui'ing e.xercise, of under- 

 lying and diverging muscles. It is here maintained tliat 

 they fairly bear the name of pedometers because of the 

 close way in which the degree of locomotive activity is 

 registered according to the persistence, size, and con- 

 stancy of these otherwise uncalled-for arrangements of 

 hair. When a few horses in the act of trotting are 

 watched, and the accompanying diagram of the main 

 muscles of the horse and the commonest whorls, featherings 

 and crests are borne in mind, it is seen at once that the 



Fig. l.-Side View of Horee: A, B, C, Inquinal Wliorl, Feathering, and Crest; D, E, F, Gluteal Whorl, Feathering, 

 and Crest (very rare); I, H, G, Axillary or Po&t-humeral Whorl. Feathering, and Crest; J, K, L, Upper Cervical Whorl, 

 Feathering, and Ciest; M, N, O, Middle Cervical Whorl, Feathering, and Crest; P, Lower Cervical Whorl. 



a direction slightly concave forward. It commences at 

 the fold of skin, which passes from the lower part of the 

 abdomen to the hind-limb, by a whorl or vortex of hair. 

 This radiates and expands into a bilateral and symmetrical 

 expansion shaped like the barbs of a feather. The latter 

 proceeds upwards in the inguinal hollow as far as the 

 level of the iliac crest, where a projection covered by muscles 

 is always to be recognised, and here it abruptly terminates 

 in a ridge or crest. The crest is very noticeable in all 

 domestic horses, and lies parallel with the long axis of the 

 trunk. Above it, and on either side of it, are seen the 

 hair-streams from the back of the animal, breaking away 

 like two currents of water on either side of an outstanding 

 rock, the anterior stream passing with a wide curve 

 forwards and d.iwnwards along the side of the abdomen. 



very conditions required to produce some departure from 

 the ordinary slope of the hairs in the inguinal hollow are 

 present, if indeed it be a possibility that underlying 

 divergent muscular traction should intluence the course of 

 the living growing stream of hair on that portion of the 

 skin which lies over the area affected. If also a few 

 horses be watched as to the degree and extent of the 

 "jolt" which occurs at every quick step, and the sharp 

 limitation of tliis to the area included in that of the whorl, 

 feathering and crest — ceasing, as it does, abruptly and 

 significantly at the level of the crest of the ileum — the 

 modus operandi is very clear. The forward range of the 



* (I) Proc. Zool. Soc. Land., 190O,p. 6S2. (2) " Use-inheritance" : 

 A. & C. Black, London, 1901. (.3) Proo. Zool. Soc. Land., I90i, p. 156. 



