530 CHARLES W. HARGITT 
structure, details of which have been elaborately developed by 
Owen (48) whose well-known ‘Homologies of the vertebrate 
skeleton’ is its best expression. But to these naturalists homology 
meant likeness of structure merely, with the implications of ideals 
and design. To naturalists of the later period the conception 
took on an infinitely larger scope and significance. Like the for- 
mer, they were free to accept likeness of structure as an index of 
homology; but following the blazed trail of Lamarck and St. 
Hilaire, they conceived in the doctrine the key to lineage. To 
them homology involved kinship; and ‘archetypes’ as such had 
no vital meaning. It is not strange that, under the masterful 
hand of Darwin, the newer doctrine gave to biologists a working 
hypothesis comparable with that of gravitation, and at once 
placed biology on the foundation of scientific certitude. 
To naturalists of both periods must be ascribed well deserved 
praise. Both sought in the most conscientious and critical manner 
to discern the facts of homology. Among both were those of 
divergent and conflicting views,' von Baer and Cuvier versus 
Lamarck and Hilaire; Agassiz versus Darwin. In both were 
elements of important truth; in both were extremes of mischiey- 
ous error. It is not the purpose to undertake any critical review 
of the phases of conflict involved in these antithetic aspects of 
one of the most profound of biological doctrines; but rather, 
ignoring extremes of the earlier period, whose errors have largely 
gone into oblivion, to point out in briefest way wherein, under 
the ardent impulse of the newer view, something of extravagant 
over-valuation has come to have a retarding and mischievous 
influence upon biological thought and progress. It hardly need 
be said that in this matter attention will be directed to those points 
in particular which have come under my own lines of research. 
A similar duty has been ably performed upon a larger scale by 
several brilliant authorities, among them Wilson (’94), Morgan 
(03), Montgomery (’06). 
a. The germ-layers. No occasion exists for a review of the 
origin of the conception of germ layers developed through the 
work of Wolff, Pander, von Baer, Remak and KOlliker. It is 
sufficient to my purpose to cite the astute observation of Huxley 
