172 CHARLES MIDLO AND HAROLD CUMMINS 



case is borne out by an actually high dermatoglyphic varia- 

 bility in Pongidae and Homo. Accordingly, our analysis of 

 dermatoglyphic variation represents an evaluation of the state 

 of the pads only during the formative period of the dermato- 

 glyphics. There is probably an essential correspondence in 

 the fetal and adult characteristics of pads in those primates 

 which exhibit the most prominent pads in the adult (some 

 prosimians and most monkeys). 



If the volar pads are to be regarded as primitively as- 

 sociated with walking, then their attainment of softer con- 

 sistency and their subsidence are modifications attending the 

 acquirement of the prehensile function, either supplementing 

 or superseding the original walking function. It may be as- 

 sumed, even in the absence of observations on the fetuses of 

 all primate genera, that there is variation among them in 

 the chronology of pad development. In a form presenting 

 earlier and more nearly complete suppression of the fetal 

 pads the inference is that this form stemmed from an ancestry 

 of walkers at a period earlier than the splitting of the line 

 leading to forms which retain pads for a longer period of 

 the fetus; these forms in turn would be phylogenetically 

 farther removed from the common ancestry than primates 

 which retain permanently well defined pads. 



The foregoing deductions would be invalidated if it were 

 proved that the pads are not subject to Dollo's principle of the 

 irreversibility of evolution. It is conceivable, though not 

 demonstrable, that volar pads, having undergone the modifi- 

 cations brought about by arboreal existence and prehension, 

 might be restored to original primitiveness by resumption of 

 the walking habit. Since observations on human fetal pads 

 indicate that pads having primitive qualities appear tem- 

 porarily, the pads should not be considered as irrevocably 

 suppressed even in a form presenting but little indication 

 of them in the adult. It might be even conjectured that in a 

 form such as man the greater retention of primitive char- 

 acteristics of fetal pads in the sole is a result of newly acquired 

 walking habit, the acquisition coming too late in the evolu- 



