DEVELOPMENT OF AMMONITES, 215 
first. Thus searching through the strata from below 
upwards, we sce modification after modification begin- 
ning at the outer part of the Ammonites, and advancing 
towards the centre of the discs. The innermost convo- 
lutions often resist these innovations with great persis- 
tency, so that we usually find upon their surface several 
of these states of development closely compressed, as 
the shell of the individual Ammonite begins with the 
old morphological type, and then adopts the modifica- 
tions in the same order in which they follow in vast 
periods in the geological development of the groups 
concerned.” 
“The Ammonites,” he says moreover, “thus obtain 
at an advanced and maturer age—only when they have 
gone through the development inherited from their 
parents, and as much as possible in the same manner as: 
their parents—the power of modifying themselves in a 
new direction, that is to say, of adapting themselves to 
new conditions; yet these modifications may then be 
transmitted to the offspring, so as to appear in each 
subsequent generation a trifle earlier, until this phase of 
development in its turn characterizes the greater portion 
of the period of growth. But this last and longest 
phase of development scarcely ever suffers itself to be 
supplanted by new ones, formed in like manner; heredity 
operates so powerfully, that a period of development 
thus once predominant, is repeated in the infancy of the 
Ammonites, even though but slightly indicated. Hence 
in an individual Ammonite from a recent stratum, the 
periods of development compressed and forced back 
upon the innermost convolutions, must appear in the 
same succession in which they wrested the dominion 
