Palaeontological Speculations.—Gratacap. 295 
cephalon, the increase in size of the free cheeks, and the re 
ceding of the facial suture towards the axis. Such a meta- 
morphosis has all the character of inevitableness. It does not 
seem to be fortuitous, secondary, or precipitated by such vary- 
ing adventitious influences as environment or survival selec- 
tion. 
The examples of evolution of the Cephalopoda have been 
reviewed by numerous authors, though its establishment is 
due to Quenstedt, Von Buch, Brown, Hyatt. A series of 
changes from straight to arcuate to coiled and involute shells 
has been made out with a reversion in pathological or senile 
periods, in the Jura and Cretaceous. The changes have been 
thus summarized by Hyatt: “The efforts of the Orthoceratite 
to adapt itself fully to the requirements of a mixed habitat 
gave the world the Nautiloidea: the efforts of the same type 
to become completely a littoral crawler developed the Am- 
monoidea. The successive forms of the Belemnoidea arose in 
the same way; but here the ground-swimming habitat and 
complete fitness prevailed, for that was the object, whereas 
the Sepioidea represent the highest aims as well as the highest 
attainments of the Orthoceratites, in their surface swimming 
and rapacious forms.” 
Paleontologically regarded the habitat of these derivative 
forms does not seem so contrasted as to lead to efforts of adap- 
tation violent enough to produce these changes, and in the evo- 
lution of ammonoid forms from goniatitic, the assumption of 
septal modification seems to have no relation to either habitat 
or effort. | 
Is there not rather implied here a “law of growth.” The 
“laws of growth” have been insisted on by Eimer and Piepers 
(See Die Farbenevolution bei den Pieriden, M. C. Piepers), 
although their English reviewers have had little patience with 
them. Piepers has taken some pains, and apparently not al- 
together unsuccessfully, to show that in the course of color 
evolution in the Pierids, starting from an original red the pro- 
cess of color change is toward white which final stage is 
gradually attained by paling through orange and yellow, or 
through an intermediate black. The view of Piepers is weil 
described in the language of his reviewer. He believed in 
“this inevitable tendency arising from an internal impulse to- 
