No.424.] LATENT OR POTENTIAL HOMOLOG Y. 265 
and “convergence,” which; as we have seen, may affect 
absolutely non-homologous structures. Homoplasy should be 
confined to structures in which there is an element of homology. 
Independently of Lankester (that is, not familiar with his 
paper) I had therefore reached a similar conclusion through 
years of observation in paleontology. I would now like to 
expand an idea which he also lightly suggested in 1870 in 
the words, “or on parts which for other reasons show a likeness 
of material to begin with.” 
Tue Law or HOMOPLASY AS IN PART IDENTICAL WITH 
DEFINITE OR DETERMINATE VARIATION. 
As observed in the evolution of the teeth especially, homop- 
lasy appears to be of very great importance, not on the tech- 
nical grounds of uniformity in nomenclature, but because it 
seems to coincide with the principle of definite or determinate 
evolution, a principle which may be of wider application." 


Homo, showing independent or 
+h R, 1 
1 
p F 
ti af the hi ne. ky fi 
y : ^y, 


D 
From the time of the “ Origin of Species ” it has been admitted 
that evolution, so far as it depends upon variation, is not in 
every possible direction, but is limited to certain changes, 
the expression of certain hereditary or constitutional causes 
which we do not in the least understand. The evolution of 
the teeth of mammals enabled me in 1889 to give many con- 
crete illustrations of this principle and to show that variation 
is hardly the proper term to apply to rudiments which do not 
arise in a variable but in a fixed manner. 
1 See especially the correspondence of Darwin and Asa Gray; also Osborn, 
The Palzontological Evidence for the Transmission of Acquired Characters, 
Nature, Jan. 9, 1890; the Orthogenesis and Orthoplasy of Eimer, Lloyd Morgan 
aldwin ; Baldwin’s Dictionary of Philosophy and Psychology, vol. i, p. 243- 
