422 The American Naturalist. [Máy 
With reference to Mr. Carey’s first proposition that these 
metapodial crests are produced during the life of each individ- 
ual by the necessary interaction of parts, it appears to me to 
be a very simple one indeed. If they are produced, by pres- 
sure during the lifetime of each individual, and are not 
inherited, then clearly we should find the crests absent in new 
born animals that had never walked, and in which the meta- 
podials had not been subjected to any impact or pressure 
whatever. I have taken the trouble to examine a number of 
such examples in which the distal ends of the bones were entirely 
cartilaginous, and I find that the keels and grooves are as 
well developed as they are in the adult animal. I will cite 
one case in particular in which I happen to know the history 
completely. During the past winter, a young hippotamus was 
born in the Zoological Gardens in Central Park, and it was 
stated to have been a premature birth; the animal lived but- 
twenty-four hours, and I was informed by the keeper that it 
never stood upon its feet. An examination of the feet shows 
that the distal ends of the metapodials are entirely cartilagi- 
nous, and in them the keels are as well prefigured in cartilage 
as they are performed in bone in the adult animal. Ihave 
also found the same to be true of newborn rabbits and guinea- 
pigs. In another case of a young buffalo calf preserved in the 
American Museum Collection, the distal keels of the metapod- 
ials are complete notwithstanding the fact that the epiphyses 
of all the bones are very imperfectly ossified. This evidence, 
it appears to me, effectually disposes of the question of the 
production of these structures during the lifetime of the indi- 
vidual. They are as truly inherited as is the number of digits 
or any other important organ in the animal economy. 
Mr. Carey further states in his concluding remarks that 
“ Plasticity of bone, using the word plasticity not in a physical 
sense merely, but to include absorption under pressure, will 
‘probably account for much structure in the foot and elsewhere, 
especially in connection with the joints and in the field of 
variation and correlation.” Now just what Mr. Carey means 
by “absorption under pressure” is not clear to my mind. If 
he means a process similar to that of the absorption of the roots _ 
