1893.] Evolution of Metapodial Keels of Diplarthra. 421 
A NEW THEORY OF THE MECHANICAL EVOLUTION 
OF THE METAPODIAL KEELS OF DIPLARTHRA. 
By J. L. Wortman, M. D. 
In the last number of the Journal of Morphology, Mr. Aus- 
tin Carey gives the results of his studies in the foot structure 
of the Ungulates. A fair statement of his main conclusions, 
or rather perhaps the pith and substance of his argument is to 
be found in the concluding sentence of his article which reads 
as follows: “ That the lines of evolution have progressed with 
but few useless side variations seems to be the uniform testi- 
mony of paleontologists; but that race changes follow those 
produced in individual life, or that they are directly caused 
by their mechanical surroundings, I do not think has been 
satisfactorily shown.” 
It is not my intention to enter here into a criticism or gen- 
eral discussion of the points this author has raised in his 
argument, nor will I undertake to discuss at this time the 
broad question of the transmission of acquired characters. I 
do, however, wish to say a few words upon the question of the 
production of crests and keels upon the distal extremities of 
the metapodial bones. Upon this point Mr. Carey says, (p. 
341) “The crests and grooves on the lower metacarpal ends 
in some forms, produced apparently in relation to the sesamoid 
bones, is one of the most marked examples of probable 
mechanical evolution.” “But before such structures can be 
said to prove the inheritance of acquired characters, the ques- 
tion should be tested whether they are not produced some- 
where in the history of each individual by the necessary 
interaction of parts.” He further adds in a footnote that 
“The crests in certain highly specialized forms, like the horse 
and deer, reach round to the anterior face of the bone and 
apparently cannot thus be interpreted or assigned to any 
mechanical origin that is obvious.” 
