342 Mr. E. R. Lankester on the use of the term “ Homology.” 
XXXII.—On the Use of the Term “ Homology.” 
By E. Ray LANKESTER. 
To the Editors of the Annals and Magazine of Natural History. 
GENTLEMEN, 
Whilst acknowledging with pleasure Mr. St. George Mivart's 
recent paper “ On the Use of the Term * Homology, " I think 
that I cannot have been sufficiently clear as to the use of the 
term homogeny in my own article, since he speaks of “ ances- 
tral” and “ developmental" homogeny. I proposed to signify 
by “ homogeny ” simply what he terms “ ancestral homogeny. " 
Structures which he would call * developmental homogens,” 
if they are not also ancestral homogens, do not come under 
my term homogen at all, but are homoplasts. The fact of the 
absence of ancestral relation at once removes them from 
the category of homogens. The individual cranial bones of 
man are not all homogenous, each for each, with those of the 
osseous fish: but they are homoplastic; d. e. conditions other 
than direct heredity have determined a close agreement of 
arrangement. 
The similarity of the development of so-called homologous 
tions of the organism to its conditions of existence; and in 
this way whole pages of history are blotted out or reduced to 
I remain, Gentlemen, 
ruly yours, 
E. Ray LANKESTER.- 
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