September 23, 1904.] 



SCIENCE. 



403 



very frequent, strong, opposing muscular trac- 

 tions. In both the frontal and pectoral re- 

 gions of the horse the whorl is said to he 

 absolutely constant, and in the latter region, 

 it is accompanied by a feathering and crest, 

 thus involving a reversal of the hair over a 

 portion of the pectoral area. In other mam- 

 mals, even those so closely related to the horse 

 as the mule and ass, pectoral whorls are of 

 much less frequent occurrence. The cervical, 

 axillary and inguinal regions of the horse 

 show whorls with a greater or less degree of 

 constancy, and statistics indicate a correspond- 

 ence between the development of locomotive 

 power, on the one hand, and both the degree 

 of perfection and the constancy of occurrence 

 of these whorls, on the other, a correspondence 

 the significance of which is of course empha- 

 sized by their infrequent occurrence in re- 

 lated forms of less highly developed loco- 

 motive power. Thus Kidd looks upon these 

 whorls as actual ' pedometers,' and by way of 

 emphasizing their significance draws a strik- 

 ing comparison between the horse and the 

 zebra, which rarely exhibits any whorls. 

 " These two animals carry about on their 

 hairy coverings indubitable records of their 

 habits and those of their near ancestors." 



To the action of the panniculns carnosus 

 of the back in shaking oil flies and other in- 

 sects are attributed the whorl and feathering 

 which occur upon the spinal area of the lion, 

 ox, girafie and larger antelopes. Statistics 

 are given to show the correlation of this phe- 

 nomenon with a heavy mane and long tail, 

 devices for removing insects from other re- 

 gions. 



In the gluteal region of some animals, par- 

 ticularly certain breeds of dogs, whorls are 

 described which, contrary to the principles 

 previously set forth in defining a whorl, are 

 attributed to the passive influence of external 

 pressure resulting from the frequently as- 

 sumed sitting posture. In none of the cases 

 which happen to have come under my own 

 observation, however, does this feature involve 

 a divergence of hair (the essential element of 

 Kidd's whorl) the figure being distinctly a 

 convergent spiral (in Voigt's terminology a 

 ' convergierende Wirbel ') corresponding more 



closely, as is shown later, to Kidd's definition 

 of a tuft. Moreover, the sitting position of 

 dogs is, so far as I have observed it, a crouch- 

 ing upon the hind legs, often with the ischial 

 prominences hardly in contact with the ground, 

 the weight being borne mainly upon the tarsus 

 and foot. 



Tufts, which of all the critical area phe- 

 nomena are the most rare, involve always a 

 convergence of the hair towards a point. 

 Among the cases cited are those of the rare 

 gluteal tuft of the horse said to be caused by 

 the friction of the kicking-strap, and the more 

 common gluteal tuft of the domestic os, at- 

 tributed to the habit of flicking the tail for 

 the purpose of removing flies. There seems 

 to be a decided discrepancy between these 

 illustrations, with their explanations, and the 

 general statement (p. 22) that tufts are the 

 result of ' frequent, converging muscular ac- 

 tion.' Even the tufts which are mentioned 

 as occurring in the inguinal region in horses, 

 although attributed to the action of the great 

 oblique muscle, are not shown to be due to 

 convergent muscular action. 



These two regions, viz., the gluteal and in- 

 guinal, are the only ones upon which Kidd 

 has found tufts. He has, however, overlooked 

 several others of common occurrence, both on 

 the horse and on other domestic animals. 

 Such, for example, is the very common 

 olecranal tuft which is well shown by short- 

 haired dogs and is of practically constant oc- 

 currence in the human fetus. 



A separate chapter is devoted to the consid- 

 eration of the critical areas of man because 

 man is the species the habits of which are 

 the most completely known. Kidd finds none 

 of the peculiarities of hair direction in man 

 dependent upon locomotive activity. The 

 numerous deviations from the primitive hair 

 direction are, therefore, attributed not to 

 motor phenomena, but rather to the influence 

 of external forces. 



The very ancient habit of sleeping or rest- 

 ing upon the back or side with the head and 

 shoulders slightly elevated upon some sort of 

 pillow is said to be responsible for many of 

 man's peculiarities of hair direction. Among 

 these are the partial reversal upon the deltoid 



