464 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
but he failed to receive enlightenment by examination of the numer- 
ous skeletons he had made. Those skeletons, pregnant with signifi- 
eance for the future, had no meaning for Cuvier; he never learned 
how to utilize them for the fishes as he did those of the mammals. 
His colleague and successor, Valenciennes, in the great “ Histoire 
Naturelle des Poissons,” was equally unappreciative of the impor- 
tance of comparative osteology for comprehension of the mutual re- 
lations of the groups of fishes. 
CUVIER’S SUCCESSORS. 
The same defect in method or logic that characterized Cuvier’s 
work was manifested by his great English successor in range of 
knowledge of comparative anatomy, Richard Owen. His families, 
for the most part, were the artificial assemblages brought together 
by zoologists on account of superficial characters and too often with- 
out rigorous attention to the applicability of the characters assigned. 
Much better was the work of the greatest naturalist of all, Johannes 
Miiller, who advanced our knowledge of the systematic relations of 
all classes of vertebrates as well as invertebrates. But all were un- 
able to free themselves from the incubus of the popular idea that all 
branchiferous vertebrates formed a unit to be compared with birds 
and mammals. Several propositions to segregate, as classes, Am- 
phioxus and the chondropterygians had been made, and Louis Agas- 
siz deserves the credit of claiming class value for the myzonts or 
marsipobranchs as well as the selachians. But it was left to Ernst 
Haeckel, a pupil of Miiller, still happily living, to divest himself 
entirely of ancient prejudices and appreciate the interrelationship of 
the primary sections of the vertebrate branch. He for the first time 
(1866) set apart the amphioxids in a group opposed to all other ver- 
tebrates, then docked off the marsipobranchs from all the rest, and 
collected the classes generally recognized in essentially the same man- 
ner as is now prevalent. We may differ from Haeckel as to his 
classes of fishes and dipnoans, but his correctness in the action just 
noticed will be conceded by most, if not all, systematic zoologists 
to-day. 
EMBRYOLOGY. 
While Cuvier was still flourishing, a school of investigators into 
the developmental changes of the individual in different classes, and 
among them the vertebrates, was accumulating new material which 
should be of use to the systematic zoologist. Chief of these was Karl 
Ernst von Baer. In various memoirs (1826 et seq.) he subjected the 
major classification of animals to a critical review from an embryo- 
logical point of view, recognized, with Cuvier, the existence of four 
distinct plans which he called types and characterized them in em- 
