Jaekel on Orthoceras. — Rnedcmann. 201 
I beg to add the following theses on the relation of the 
cephalopod to the other mollusks : 
"11. I consider as progenitors or as proseries of the 
cephalopods, the conularias, in which the body form and shell 
secretion of the orthoceratites was inaugurated and the form- 
ation of four gills, which it would be difficult to derive from 
the body form of the cephalopods, was established. Lateral 
members of this proseries we find in the Hyolithidse, which 
present in their incomplete formation of septa and the well 
developed formation of opercles, certain analogies to the ceph- 
alopods. (The aptychi are herein considered as cuticular 
calcifications of the hood, which in Nautilus serves for ex- 
ternal closure of the ostium,)'' 
Professor Jaekel made some general remarks on the form 
and purpose of these theses from which we learn that the form 
in which they are presented is simply to invite discussion. This 
appeared necessary because the biological consideration of 
these extinct mollusks has gradually fallen too far behind their 
morphologic and systematic treatment, and it can be hardly dis- 
puted that with .such aberrant types as the orthoceratites and 
belemnites an understanding of their organization can be at- 
tained only by thorough consideration of their mode of life. 
As the meaning of changes in organs can be ascertained only 
in a biologic way, and while the paleontologist has perpetually 
to deal with processes of alteration, there is also in this field 
the necessity of the biologic mode. 
In explanation of theses i and 4, which refer to the organ- 
ization of the orthoceratites, we find the following remarks : 
"With the view hitherto current that the orthoceratites 
moved through the water like the slender squids of the pres- 
ent (Oigopsidse), that hence the apex of the orthoceracone was 
directed forward when in motion and served as a water-cutter, 
the following parts of their organization seem to me to be spec- 
ially at variance : 
"a) The calcareous shell of the orthoceratites is much too 
thick and heavy for a pelagic habit, moreover it is in some 
forms often loaded with special calcareous secretions. 
"b) The external sculpture of the shell excludes the possi- 
bility that the latter could have been imbedded in the fiesh of 
the body ; hence active swimming organs could protrude only 
at the apertural end of the shell (osiimn). 
