﻿402 



phylum, it would not be so closely parallel to the ontogenic cycle, 

 which we know to be subject to great variations in accordance with 

 the surroundings of the individual or species. 



The standard of reference in bioplastology is the ontogenic 

 cycle, and this should be studied first in every group. Without 

 a full knowledge of this, the morphology of the group cannot be 

 properly translated, nor can the forms be taxonomically treated 

 with reference to their natural relations. This branch of research 

 aims to complete Von Baer's law and Louis Agassiz's great discov- 

 ery of the correlations of palingenesis and phylogenesis, and it, 

 therefore, asserts an equal utility for the metamorphoses of the 

 nepionic, neanic, ephebic, and gerontic stages, provided these be 

 applied in each group according to the ontogenetic development of 

 the cycle in the zoon and its phylogenetic evolution in the same 

 group. 



III. Ontogenetic Stages. 



My own researches have led me to the conviction that subdivis- 

 ion of the developmental phenomena of the nepionic, neanic and 

 ephebic stages are necessary, and for obvious reasons I shall take 

 my illustrations wholly from the shell-covered Cephalopoda. 



Those who do not believe that there was a protoconch in nauti- 

 loids will have to reconstruct this part of the nomenclature in ac- 

 cordance with their own views. Having been reproached by Prof. 

 Blake in his address before the Geologists' Association in 1892 in 

 London for holding to this opinion, it is only necessary for me to 

 point again to the new evidence with regard to the existence of the 

 protoconch given in the Introduction to this memoir. 



Granting, therefore, that the conch begins with the nepionic 

 stage, the first part of this period is the ananepionic substage. This 

 substage is more or less similar in all the, nautiloids on account of 

 the existence of the cicatrix on the point of the apex of the conch and 

 the surrounding comparatively smooth area which is, as a rule, ellip- 

 tical, the apex being in most forms of Nautiloidea, when seen from the 

 side, like a broad cup, and in section a laterally compressed ellipse, 

 the vertical or ventro-dorsal diameter being the longest. 



This substage is frequently figured in the plates of this memoir, 

 and has been well shown in figures of several species, in the Gene- 

 sis of the Arietidce, pp. 10, 11, and in Nautilus pompilius in Fossil 



