NOMENCLATURE OF STAGES OF GROWTH AND DECLINE. 19 
The ephebolic characters are as a rule inherited or homogenous within the 
special series in which they originated, but are not transmitted from one series 
to another except through the medium of the nealogic stages of what we have 
called the tertiary radicals, and they are not, so far as we know, ever concen- 
trated in the earliest larval or nepionic stages; they occur too late in the 
history of types. 
We classify in the nealogic and ephebolic stages such characters as follows: 
the sharply defined ridge-like pile and tubercles, the channels with their lateral 
ridges, and keels, and especially the hollow keel, the highly developed rostrum 
of the higher suborders, especially Ammoniting, the lateral lappets of the aper- 
tures, and the branching marginal lobes and saddles of the sutures of suborders 
above Goniatitine. Speaking in a general way, we should include in these 
categories those progressive characters which appear late in the life of the 
shell among the higher suborders, and at the acme of their development in 
time, which are not found in the stock of discoidal radical forms. When the 
shell began to assume the ribs or pile, as we prefer to call them, the nealogic 
period may be said in a general way to have been entered upon. It has been 
found that these stages of growth indicated genetic relationship with radical 
forms, which were not infrequently merely different genera or species within 
the limits of the same family, and often occurred on the same or only slightly 
different horizons. The nealogic stages of the higher Ammonoids, Ammoni- 
tine and Lytoceratine, have not the constancy and general importance of the 
nepionic stages, but are transient in the history of the types, appearing and 
disappearing in the same limited series of forms. They consist of the less im- 
portant modifications which first appeared in the adolescent or adult stages at 
a late period in the history of a type, and were then inherited in the nealogic 
stages at earlier ages in successive species of the same series, according to the 
usual action of the law of acceleration. The nealogic category cannot be as 
definitively separated from the characteristics of adults as from those of the 
larve. Their first appearance in adults indicated the establishment of a new 
species in any given series, since they are invariably differences so far as their 
predecessors and congeners in the same series are concerned. However much 
they may represent or reproduce the characters of species in other series, they 
are essentially differentials as regards the adult stages of ancestral species of 
the same series. Thus the nealogic characters are as a rule ephebolic, and not 
nealogic, in origin among the Cephalopoda, and usually become nealogic through 
inheritance. We shall have frequent occasion farther on to call in the evidence 
of the ephebolic stages, and to show, as in the Endoceratide, that, as a rule, 
characteristics originated in this stage of growth, as indeed must have been the 
case with the caecum and the microsiphon. 
At the termination of the progressive stages, which ended with the full 
development of the ephebolic characters, the first stage of decline, or the gera- 
tologic period, began to make its appearance, and became more and more appar- 
ent as the specimens advanced in age. It was found that, as has been observed 
1 See, for secondary and tertiary radicals, p. 22 et seq. 
