212 The American Geologist. ^'^p'*'' ^^'^^■ 
been a time when the straight cones or their immediate an- 
cestors predominated, to the exckision of the coiled and per- 
haps even of the arcuate types." 
If now the orthoceratites were actually the earliest cephal- 
opods we may, by application of the general principle regard- 
ing the origin of life, mentioned above, infer that they were 
certainly not free swnmming forms, but either sluggish crawl- 
ers or wliolly sessile. As the structure of their shells would 
seem to exclude the crawling habit, the sessile would remain 
by exclusion. 
On the other hand, it can not be denied that facts present 
themselves which do not corroborate the theory of the sessile 
mode of life of Orthoceras. It becomes evident from Jaekel's 
remarks and explanations that the presence of "air-chambers" 
is considered necessary to relieve the apex of the shell from 
the weight of the shell and animal by the upward pressure 
of the contained air. The current view is thereby retained that 
the chambers of the cephalopod shells were "air-chambers " 
This view seems, however, by no means established, for Verrill 
(see Zittel-Eastman. Text book of Palentology, p. 508) states 
that the chambers of Nautilus stand by way of the siphuncle 
and pericardium in direct connection with the gill cavity, and 
adds : "Thus sea-water can readily pass into or out from the 
chambers of the shell, to equalize pressure at varying depths, 
as in most marine MoUtisca. These chambers are unquestion- 
ably filled with fluid under normal conditions. But living as 
the animal does under pressure at considerable depths, the fluid 
in the chambers is saturated with the gases in solution. When 
the Nautilus is rapidly brought to the .surface, some of the gtis 
is liberated in consequence of diminished pressure, and must 
occupy part of the space within the chambers by forcing out 
some of the fluid. Hence the shell will float until the free gases 
within the chambers are absorbed or otherwise eliminated. 
There is no evidence that free gases are ever naturally present 
in the living chambers during life." 
If the living Nautilus has its chambers filled with water, 
the inference is that the extinct cephalopods had it likewise. 
Hyatt has therefore properly proposed the non-committal term 
"cameras" for the compartments of the cephalopod shell. The 
fact of the filling of the chambers with water would, however, 
