XVIII 
ON SPECIES AND RACES, AND THEIR. ORIGIN 
Proceedings of the Royal Institution of Great Britain, vol. tit. 1858-62, 
pp. 195-200. (friday, February 10, 1860.) 
THE speaker opened his discourse by stating that its object was 
to place the fundamental propositions of Mr. Darwin’s work “On the 
Origin of Species by Natural Selection,” in a clear light, and to con- 
sider whether, as the question at present stands, the evidence adduced 
in their favour is, or is not, conclusive. 
After some preliminary remarks, in the course of which the speaker 
expressed his obligations for the liberality with which Mr. Darwin 
had allowed him to have access to a large portion of the MSS. of his 
forthcoming work, the phenomena of species in general were con- 
sidered—the Horse being taken as a familiar example. The dis- 
tinctions between this and other closely allied species, such as the 
Asses and Zebras, were considered, and they were shown to be of two 
kinds, structural or morphological, and functional or physiological 
Under the former head were ranged the callosities on the inner side 
of the fore and hind limbs of the Horse—its bushy tail, its peculiar 
larynx, its short ears, and broad hoofs; under the latter head, the 
fact that the offspring of the horse with any of the allied species is a 
hybrid, incapable of propagation with another mule, was particularly 
mentioned. 
Leaving open the question whether the physiological distinction 
just mentioned is, or is not, a universal character of species, it is 
indubitable that it obtains between many species, and therefore has 
to be accounted for by any theory of their origin. 
The species Eguus caballus, thus separated from all others, is the 
centre round which a number of other remarkable phenomena are 
