Jackel on Orthoceras. — Ruedemann. 199 
PROFESSOR JAEKEL'S THESES ON THE MODE 
OF EXISTENCE OF ORTHOCERAS AND 
OTHER CEPHALOPODS. 
By Rudolf Ruedemann, Albany, N. Y. 
Professor Otto Jaekel presented at the February (1902) 
meeting of the Deutsche Geologische Gesellechaft the follow- 
ing theses, which were discussed at the March meeting and at 
a special meeting in April.* 
"i. We should not conceive of the orthoceratites as free- 
swimming organisms, but, like the colularias, actually sessile 
in such a fashion that their chambered shell grew upward from 
a bell-shaped fixed embryo-chamber and throughout life re- 
tained flexible connection with this by means of - conchioline 
secretions. 
"2. The formation of septa and camerse served, as in corals, 
Hippurites and some sessile, erect gastropods, to lift the body 
above the sea bottom (growing upward by sedimentation), 
without necessitating an essential alteration of its form, and 
also to facilitate the upright posture of the shell and its animal 
on a relatively small base. 
"3. The siphonal cord then appears to be that portion of the 
body which is reduced by the formation of camerse. As com- 
pared with other animals bearing chambered shells its form- 
ation becomes intelligible by the fact that the body grows only 
secondarily from the original fixation or embryonal chamber, 
and that the latter was hence an integral part of the original 
body. 
"4. The siphonal calcareous secretions (obstructive rings 
and endosiphonal calcareous deposits in the lowermost part of 
the shell of the endoceratites) serve to ballast the body so as to 
counterbalance the formation of air chambers, which latter 
guarantee an upright position. 
"5. The involute Nautiloidea in the restricted meaning, 
have discarded fixation, either from the beginning or in later 
stages of their development. Their protoconch consisted of 
conchiolin and was therefore not capable of preservation. For 
this reason, it cannot be determined whether it was retained by 
* Published in Zeitschr. der Deutscben Geol. Gesellsch, 54 Bd., 1902, p. 67- 
101. 
