604 On the Laws of Digital Reduction. [ October, 
creased, while the ento-cuneiform and navicular are greatly flat- 
tened or modified in the same way as the magnum and unciform 
of the manus and the middle and ecto-cuneiforms of the pes are 
in many ungulates, or as is the cuboid in the kangaroos. 
In ungulates the third and fourth toes become functional, the 
second and fifth either disappearing or else assuming the office of 
lateral supports. In the jumping mice ( Dipodide) the second, 
third, and fourth of the hind feet are the functional ones ; in one 
species three toes are all that remain; in another with four the 
fifth, a rudimentary one, does not reach the earth; and in another 
species with five the first and fifth toes are rudimentary. In 
these three animals, then, of one family and only generically sep- 
arable by the difference in the number of toes, we have a case in 
living animals resembling the “demonstrative evidence” of 
Professor Huxley drawn from fossil horses’ toes, which so far as 
the necessity for time is concerned shows that creatures of almost 
identically the same habits and structure may be cotemporaneous, 
yet differing widely in the number and length of the hind toes. It 
indicates, it seems to us, that toe modification goes on at greatly 
varying rates. In the kangaroos the fourth and fifth toes of the 
hind foot are most strongly developed, while the second and third 
are atrophied and used only to cleanse the fur. It may be noted 
here, also, that the toes of the fore foot of the kangaroo remain 
entirely unmodified, and much the same as is the case in the 
jumping mice, for the reason that the strains are more equally 
distributed. ; 
The Chrysochloris amongst moles offers an instance where the 
digital reduction has taken place in the anterior extremity, 
where also the mechanical strains are most frequent and severe. 
The same fact is observed in Cyclothurus, a little South Ameri- 
can arboreal ant-eater, where but two functional toes remain 
upon the fore foot. In the great ant-bear (Myrmecophaga), the 
third digit of the manus is the strongest, the others evidently oat 
dergoing reduction, while the former is being constantly 
mented by the strains to which it is subjected in obtaining age 
prey. ; cs 
The sloths of both recent and extinct groups furnish an a 
stance where the number of toes has been reduced from the 7 
ical number five tò as few as two in one pair of extremities ak 
living Cholepus. The digits also in recent species are of a 
equal length, which cannot be said of the extinct terrestrial gi 
cies, where in some cases (Mylodon and Megalonyx) consi® 
