244 



SMITH. 



[Vol. XVI. 



condensing lens to see the siphon and other internal characters 

 when the specimen is translucent. This latter mounting is well 

 suited to work in direct sunlight with a polarizing microscope, 

 for the whole field is dark except where the doubly refracting 

 calcite of the young ammonite allows the light to pass through. 



Nomenclature of Stages of Growth. 



In order to correlate ontogenic stages with generic changes 

 seen in the development of the race it is necessary to have an 

 exact scientific nomenclature. The most satisfactory, and one 

 now being generally adopted, is that given by Professor Hyatt 

 in "Phylogeny of an Acquired Characteristic."^ 



Table of Ontogenic Stages. 



Stages. Stages. 



Embryonic (i) Embryonic 



i 



Larval (2) Nepionic 



Adolescent (3) Neanic 



Adult 



Senile 



(4) Ephebic 



(5) Gerontic 



Substages. 



Protembryo 



Mesembryo 

 Metembryo 

 Neoembryo 

 Typembrj'o 

 Phylembryo 



( Ananepionic 

 ■\ Metanepionic 



L Paranepionic 



f Ananeanic 

 Metaneanic 

 Paraneanic 



( Anephebic 

 ■< Metephebic 



t. Parephebic 



r Anagerontic 



J Metagerontic 



l^ Paragerontic 



Comparison with Phylogeny. 



Phylcmbryonic 



> Epacme 



t 



Phylonepionic 



Phyloneanic 



Phylephebic \ Acme 



Phylogerontic \ Paracme 



With the embryonic stage the paleontologist can do nothing, 

 except the very last substage, or phylembryo, when the Mollusca, 

 Brachiopoda^ and other groups begin to secrete their shells; 

 but all the later stages are easily accessible in well-preserved 

 material. 



^ Proc. Amer. Phil. Soc, vol. xxxii, No. 143, pp. 391 and 397. 



