THE PAST AND PRESENT OF CUTTLE-FISHES. 765 



the Secondary age came to an end, the fullness of the Ammonite gen- 

 erations disappeared for ever. In the succeeding Tertiary period not 

 a single Ammonite of any kind occurs ; the genus Nautilus remaining 

 in the Tertiary period as it survived into the Mesozoic or middle pe- 

 riod as the sole representative of a once plentiful four-gilled popu- 

 lation. 



If the history of the four-gilled cuttle-fishes is thus plainly told as 

 having its beginnings in the Palaeozoic period, its maximum develop- 

 ment in the Mesozoic period, and its lingering presence in the Tertiary 

 period, the two-gilled cuttle-fishes may be said to possess an equally 

 interesting history. Compared with their four-gilled neighbors, the 

 two-gilled forms are late comers upon creation's scene. Not a single 

 fossil two-gilled form occurs in all the Palaeozoic period, extending 

 from the Laurentian to the Permian rocks. If they existed in Palaeo- 

 zoic seas, they have at least left no trace of their presence. Their 

 softness of body may perchance have contributed to their elimination 

 from the oldest fossil records ; but, laying aside mere conjecture, we 

 find the first fact of the past history of the two-gilled forms in the 

 presence of the fossil shells of the extinct Belemnites in the Triassic 

 rocks. The Belemnites themselves disappear at the close of the Meso- 

 zoic period ; but fossilized shells of species allied to our living Se- 

 pias occur in the Oolite ; and the internal shells of squids are found 

 in the Lias or lower Oolites. In the Tertiary rocks, Argonaut (Fig. 4) 

 shells occur in the Pliocene deposits ; the Eocene rocks also give us 

 sepia remains ; and various other two-gilled fossils {Beloptera, etc.) 

 are found in Eocene and Miocene formations. 



Briefly summarized, then, we find that the chief details in the past 

 history of the cuttle-fishes are told when we are reminded that the 

 four-gilled forms are by far the more ancient of the two groups ; that 

 they first appear in the Silurian rocks, while the two-gilled forms ap- 

 pear first in the Secondary rocks ; and, lastly, that the record of the 

 one group is the converse of the other. For, the four-gilled species 

 attained their maximum in the Primary and Secondary rocks, and have 

 practically died out, leaving the pearly nautilus as their sole represent- 

 ative in existing seas. The two-gilled race, starting in the Secondary 

 rocks, and leaving the extinct belemnites as a legacy to the past, have, 

 on the other hand, flourished and progressed, and attain their maxi- 

 mum, both in size and numbers, in the existing seas and oceans of our 

 globe. 



What ideas concerning the origin and evolution of these animals 

 may be legitimately deduced from the foregoing facts of their struct- 

 ure and distribution in time ? In the answer to such a question, asked 

 concerning any group of living beings, lies the culminating point of 

 all biological science. That the cuttle-fishes fall nominally into their 

 place in the scale of being indicated by evolution, and that in their 

 individual development, in the growth of their special organs, such as 



