Pala'ontology and the Biogenetic Law. — von Zittel. 147 
the foundation itself maybe constructed in an arbitrary man- 
ner is best shown by the unsatisfactory condition of our am- 
monite-literature. 
The time, it seems to me, has not yet arrived for the thor- 
ough reform of zoological classification on a phylogenetic 
basis. Among Protozoa and C(jelenterata there are absolutely 
no satisfactory fixed points for the phyletic arrangement of 
the various groups. Among Echinodermata it is proved that 
the correspondence in embryonic development between Astero- 
zoa and Echinozoa is evidence of a common origin ; but the 
classification of the various classes is as yet affected only to 
the smallest extent by the facts of ontogeny and phylogeny. 
The union of Bryozoa and Brachiopoda into a special phylum 
— the Molluscoidea, and their connection with the worms, de- 
pend entirely on embryological comparison : in their later 
development the two classes go so far apart that we can find 
no further parallel between them; and although the beautiful 
researches of Beecher, Clark and Schuchert on the phylogeny 
and ontogeny of the Brachiopoda will furnish a sound foun- 
dation for a new and better classification of the class, the 
first adumbration thereof is still somewhat doubtful. On the 
other hand, researches on the development of the shell in Mol- 
lusca are, without doubt, full of promise. What results we 
have to expect in this field is shown by the labors of Jackson, 
Hyatt, and Branco, though it must be confessed the}^ still af- 
ford no sutiicient basis for a classifiication of the pelecypods 
and cephalopods. 
Palaeontology has made its deepest mark in the classification 
of the Vertebrata. Here we frequently come across firml}^- 
rooted genealogical trees. Phj'logenetic and ontogenetic facts 
have effected the removal of the order Solipedia and the nat- 
ural grouping of the ungulates. The discovery of the fossil 
Condylarthra and Creodontia has brought to light unlooked- 
for relationships between ungulates and carnivores. The re- 
markable fauna of the Puerco beds contains, according to 
Cope, almost completely inditterent types, wliich cannot be 
considered either as true ungulates, beasts of prej^ or rodents, 
nor can they even be regarded as typical Cond3'larthra, Creo- 
dontia, or Lemuria: scarcely can they be dovetailed into the 
framework even of a geological classification, since they show 
relationships in the most varied directions. 
