Fig. 72.—Ammonites Jason (Reinecke). Jurassic.
Fig. 72a.—Suture of Ammonites componens (Meek), of British Columbia. Showing the complicated folding of the edges of the chambers to give strength to the shell. Cretaceous.
Fig. 73.—Cretaceous Ammonitidæ.
a, Baculites. b, Ancyloceras. c, Crioceras. d, Turrilites.
These are merely general considerations, but Barrande, in his Études Générales, goes much farther. He sums up all the known facts in the most elaborate manner, considering first the embryonic characters of the shell in the different genera, then their distribution in space and time, then all the different parts and characters of the shells in the different groups—the whole with reference to any possible derivation of the species; and he finds that all leads to the result that in every respect these shells seem to have been so introduced as to make any theory of evolution with respect to them altogether untenable. In his concluding sentence this greatest of Palæozoic palæontologists affirms that, “The theoretical evolution of the Cephalopods is, like that of the Trilobites, a mere figment of imagination, without any foundation in fact.”[18]