34 Mr. E. R. Lankester on the use of 
II.—0On the use of the term Homology in modern Zoology, 
and the distinction between Homogenetic and Homopiaete 
agreements. By E. Ray LANKESTER, B.A. Oxo 
Wuttst the adoption of the theory of evolution ~ broken 
down the notions at one time hod by zoologists and botanists 
as to the existence of more or less symmetrical classes and 
groups in the organic world, seiahlinhed by some inherent law 
of Nature which limited her productive powers to arbitrary spe- 
cial plans or types of structure, and has taught us to see, in the’ 
variously isolated and variously connected kinds of animals and 
pw simply the parts of one great genealogical tree, which 
ha 
achec l and separated from one another in athou- . 
‘aad different oe through the operation of the great de- 
r Time, yet certain terms and ideas are still in use which ` 
stroyer 
belonged to the old Platonic school, and have not been defined 
afresh in accordance with the doctrine of descent. The notion: : 
of the possibility of classifying organisms accurately by means. . . 
of division into large groups of equal value and significance, ` 
these again being divided into smaller groups of equal sub- 
ordinate value, and so on, is still almost universally preva- 
lent, although one of the first conclusions to which we are led 
by a consideration of Darwin’s doctrine i is that the groups into 
which we may be. able to = the few and scattered. samples 
of organic development known to us must be in every way 
most unequal and dissimilar, s line which we can draw in 
one case being sharp and clear , in another much less certain —— 
and definite, sometimes including a vast variety of minor. 
groups, sometimes cites definitely marked large groups, - 
in no case offering us examples of two series of forms strictly. . 
alike in extent and significance; and thus it is rendered im- 
possible to indicate the genetic relations of organisms by the 
use of the neat and symmetrical system of terms generally 
employed (consisting of kingdom, subkingdom, class, order, 
family, &c.). To do this adequately, additional terms are 
required ud. nac have been proposed), and the important 
fact has t eld in mind that we have not to search out a sup- . 
posed chefs Doaa of organisms existing in nature, ` 
but to simply indicate as clearly as we can the aaant o 
orms and the innumerably various gaps in the serie 
The term “homology” belongs to the Platonic pi: but. 
is nevertheless used without hesitation by those who reject 
the views of that school. Professor Owen (who first clearly- 
defined this term, in developing those researches into the 
agreements of essential structure under various modifica- 
tions by which the biologists of the first part of this cen- - 
