DISTRIBUTION OF ORGANISMS. 



183 



istence. These animals are to be supposed as an ultimate form, 

 reached, not through the medium of all the lower molluscan 

 orders, but only of one ; and with respect to that one, it so 

 happens that, though possessing hard parts of such delicacy as 



FIG. 98. 



FIG. 99. 



Sepia cfficinalis, or Common Shell of Nautilus pompilius, cut open to 

 Cuttle-fish. shoio the chambers and the siphon. 



to have little chance of preservation, relics of it have been dis- 

 covered as far down as any cephalopodous remains. 1 This 

 contemporaneity of the cephalopoda with the gasteropods and 

 brachiopods, it may be remarked, would be in harmony with 

 what we know of the economy of nature with respect to the 

 destructive animals. They seem to bear a relation to those 

 upon which they are destined to prey, and to be a necessary 

 accompaniment to them. Hence they would require to be 

 upon a different genetic line which actually appears, in every 

 advance of the animal kingdom, to be the case and developed 

 contemporaneously with the weaker tribes, the fertility of 

 which would otherwise produce complete anarchy. Granting, 

 then, this pedigree for the cephalopoda, it would be no anomaly 

 in our theory, although remains of mollusks inferior to them 

 should never be found lower down in any part of the earth. 



1 See page 35 of this volume. 



