162 INITIATIVE IN EVOLUTION 



circular pattern of ridges, is obviously quite unadapted for any 

 non-slipping effect of its skin, as a glance at the figure shows. 

 On the remaining segments of the digits the ridges in the main 

 slope from each side of each digit in the distal direction and fail 

 here also to obtain the best, or transverse direction for preventing 

 slipping in locomotion. The corresponding surface of D 1 is not 

 different from its pulp as to direction of ridges, and it is here to be 

 noted and admitted that when this muscular great toe is tightly 

 applied to a branch, which from its shape it must cross at a right 

 angle, the non-slipping effect of the longitudinal ridges would be 

 very effective. One must then notice that over the middle of the 

 sole of this foot the ridges have again changed their direction and 

 lie in a transverse direction. Between this and the basis of the 

 digits are three fleshy pads and an intervening area of longitudinal 

 ridges. 



The first question that arises in the attempt to analyse so 

 complex a grouping on a strange member like the foot of a loris 

 is this — what is the primary function subserved by the ridges 

 and their mode of arrangement, and what may be their secondary 

 uses ? In the book referred to I have maintained throughout, in 

 opposition to Mrs. Wilder Harris and others such as Dr. Hepburn, 

 that the sense of touch is the primary, and prevention of slipping 

 the secondary adaptation secured by the ridges. If this be true 

 (and I know it is sub judice) there is a very clear reason why the 

 ridges should be longitudinal on the tips of the digits on account 

 of the better discrimination of small objects secured by this arrange- 

 ment, though it does not well assist the loris to avoid slipping. 

 On D 1, as mentioned, the non-slipping effect is secured by its 

 ridges, and this digit is necessarily less employed for discrimination 

 than support. On the other hand the sloping arrangement on the 

 rest of the segments of D 3, 4, 5 is decidedly less effective in pre- 

 venting slipping than a transverse arrangement would have been. 

 I think I am justified in saying that too much has been made of 

 this secondary effect of the ridges in the prevention of slipping. 

 I know that the string wound round the handle of a cricket bat is 

 very effective for its purpose, but one can also understand that a 

 casual strand wound here and there on the handle as the ridges 

 are on a hedgehog's and squirrel's hand and foot would be of little 

 use for the purpose. 



On the other hand if the view may be entertained that on the 

 palm and sole of hedgehog, squirrel, loris and man, we have written 

 in rows of papillary ridges and their modes of arrangement a register 

 of long-continued flexion of hand and foot in flexion and correlated 



