1-^6 The American Geologist. Septembor, 1896 
concerning existence in earlier periods of earth history that 
can follow from ontogenetic researches alone. 
A further, indeed the practical, reason why ontogeny bears 
so slight a relation to geology and paheontology, lies in the 
fact that the earlier stages of development, with which mod- 
ern embryology almost exclusively occupies itself, are not 
capable of preservation in the rocks, and that we can, there- 
fore, never expect to find their fossil archetypes. The changes 
which occur between the embryonic and the completed adult 
stages have, at least among vertebrates, not yet received the 
attention they deserve, and it is these very changes that are 
of special interest to the palieontologist. 
In spite of these hindrances, fossil embryonic types are not 
entirely wanting, even among invertebrates. The paheozoic 
Belinuridjc are bew^ilderingly like the larva? of the living 
Lhnulus: the Pentacrinoid-larva of Anfedon is nearer many 
fossil crinoids than is the full-grown animal ; certain fossil 
sea-urchins permanently retain such features as linear am- 
bulacra and a pentagonal peristome, which characterize the 
young of their living allies; among Pelecypoda, the stages of 
early youth of oysters and Pectinid;e may be compared with 
palaeozoic Aviculida^. Among brachiopods, according to 
Beecher, the stages which living Terebratulidie pass through 
in the development of their arm-skeleton correspond with a 
number of fossil genera. Among completely distinct groups 
also, ontogenetic characters have been successfully traced. 
The beautiful researches of Hyatt, Wiirtenberger, and Branco 
have shown that all ammonites and ceratites pass through a 
goniatite-stage, and that the inner whorls of an ammonite 
constantly resembles, in form, ornament and suture-line, the 
adult condition of some previously existing genus or other. 
Series of forms whose successive links correspond with suc- 
cessive stages of development in their youngest, still existing 
representatives are the only ones that still furnish us with an 
uncontestable picture of the path along which any given as- 
semblage has evolved. These are the kind of genealogical 
trees that form the worthy goal of pahieontology. From them 
a natural system will arise of its own accord. But from this 
goal we are, unhappily, still far removed. As a rule, our pal- 
{>?ontological treas lack an ontogenetic foundation, and that 
