EVOLUTION OF FOSSIL CEPHALOPODA. 235 
their minute counterparts in youthful stages of later 
forms; in fact, he could often furnish just as exact a 
description of the form as if he had the adult genus 
before him. 
NOMENCLATURE OF STAGES OF GROWTH. 
In order to correlate ontogenetic stages with the 
generic changes seen in the development of the race it 
is necessary to have an exact scientific nomenclature. 
The most satisfactory is that given by Professor Hyatt 
in Phylogeny of an Acquired Characteristic.* 
TABLE OF ONTOGENETIC STAGES. 
Stages. Stages. Substages. Comparison with phylogeny. 
Embryonic (1) Embryonic { Protembryo ) Phylembryonic 
Mesembryo 
Metembryo 
Neoembryo 
Typembryo 
Phylembryo 
Larval (2) Nepionic { Ananepionic 
Metanepionic >} Phylonepionic 
Paranepionic 
Adolescent (3) Neanic Ananeanic 
Metaneanic 
Paraneanic 
Adult (4) Ephebic { estas 
Phyloneanic 
etephebic Phylephebic 
Parephebic 
Senile (5) Gerontic Anagerontic 
Metagerontic } Phylogerontic 
Paragerontic 
o 
& 
Parac- Acme 
With the embryonic stage the paleontologist can do 
nothing, except the very last substage or phylembryo, 
when the Mollusca, Brachiopoda, and other groups be- 
gin to secrete their shells; but all the later stages are 
easily accessible in well-preserved material. 
The best example of correlation of ontogenetic 
* Proc. Am. Phil. Soc., vol. xxxii, No. 143, pp. 391 and 397. 
