186 INITIATIVE IN EVOLUTION 



First phalangeal joints, which are prominent, present 



in all digits. 

 Second phalangeal joints absent in all. 

 Foot. Bursa under tendo achillis and over both malleoli. 



Metatarso-phalangeal joints absent on D 1; present 



on D 2, 3, 4, 5. 

 First phalangeal joints, present in all. 

 Second phalangeal joints, absent in all. 



Cercopithecus Callitrichus J. 



Hand. Dorsal surface of the whole hand shows no localised 

 bursa?, only a loose areolar tissue under the skin. 

 Styloid processes of radius and ulna no bursa?. 

 Foot. Dorsal surfaces over the whole foot similar to that 

 of the hand. 

 Bursa? present over both malleoli. 

 Well -formed small bursa? under tendo achillis. 



Cercopithecus Mono, K. 



Hand and Foot. Dorsal surfaces similar to those of J and 

 similar loose areolar tissue over styloid processes of 

 ulna and radius. 

 Bursa? over both malleoli. 

 Well -formed bursa under tendo achillis. 



Macacus JRhoesus L. 



This specimen showed more examples of bursa? than 

 the two of Cercopithecus. 



Bursa? present over styloid processes of ulna and radius, 

 also over metacarpo-phalangeal joints. 



Bursa well-marked over malleoli and under tendo 

 achillis. 



Bursa? present over metacarpo-phalangeal and meta- 

 tarso-phalangeal joints. 



No bursa? over phalangeal joints. 



Further Undesigned Experiments. 



The preceding facts as to the natural history of bursa? in man 

 and some lower Primates, even if they stood alone, are enough 

 to produce conviction as to the manner in which bursa? of all degrees 

 of perfection are formed by function, and point to the origin of the 

 initial stages of these structures. But they do not stand alone, for 

 in man there have been carried out certain undesigned experiments 

 in a similar direction, comparable to those described in the sections 

 on direction of hair and arrangement of papillary ridges. These 



