of the Term “ Homology.” 115 
tures which are broadly homogenous as well as in structures 
having no genetic affinity.” Mr. L 
words “analogy” and “analogous” in Professor Owen’s 
ployed when it is possible to determine to which process any 
given resemblance is due, ¢. e. whether it is a homogenetic or 
a homoplastic homology. ; 
Tn this way we shall have parts divisible into two categories, 
viz.: 1. Analogues; 2. Homologues. The latter will be 
further divisible, and “ homology ” will be, as it were, a generic 
term, with homogeny and homoplasy as two species under it. 
I advocate this arrangement for three reasons :— 
Because it is not possible always to discriminate between 
homogeny and homoplasy. 
2. Because there is more than one kind of homogeny ; 8o 
that if the word “ homology ” be abandoned, two terms wi 
not be enough to replace it. : 
3. Because instead of there being three relations tolerably 
equivalent in value expressed by the terms analogy, homo- 
geny, and homoplasy, homogeny and homoplasy are ve 
much more st related than is either of these two wi 
analogy,—the two latter terms both referring to relations of po- 
Sition and having nothing to do with the action of the parts 
named, the first term, on the other hand, referring to function 
exclusively. 
In the first place, it is not necessary to do more than refer to 
the great number of cases where at present it is impossible to 
. Say whether, on the theory of evolution, certain parts should 
be ed homogens or homoplasts. I quite agree with Mr. 
Lankester that * valuable results may be obtained from an 
investigation of the numerous problems of homology by the 
light s the discrimination of homogenous and homoplastic 
formations can afford ” (how fruitful have been the investiga- 
* 
tions as to the vertebral structure of the skull!) ; ini I, indeed, 
