519 



very recently have presented so obscure a problem to the naturalist, 

 is full of original observation. The history of the animals which 

 formed the Belemnites, of which it appears that nearly one hun- 

 dred species are now known, and the proofs adduced that thev 

 were provided with ink-bags like the cuttle-fish, the description 

 also of the fossil pen-and-ink fish, or Loligo, and other sections of 

 this part of the Treatise, carry our information respecting the family 

 of naked Cephalopods much further than was ever attempted in any 

 previous work. Nor should I omit to mention the exposition of an 

 ingenious theory for the use of the siphuncle and air-chambers of 

 the Ammonite, which, whether confirmed by future examination or 

 not, becomes in the author's hands the means of conveying to the 

 reader a clear and well-defined notion of the varied forms and 

 complicated structure of these shells, and of awakening a lively de- 

 sire to understand their singular organization. 



I may also recall to your notice the just and striking manner in 

 which certain physical inferences are drawn from the conformation 

 of the eyes of extinct Crustacea, such as the Trilobite. The most 

 delicate parts of these organs are sometimes found petrified in 

 rocks of high antiquity, and it is justly observed, that such opti- 

 cal instruments give information regarding the condition of the 

 ancient sea and ancient atmosphere, and the relations of both these 

 media to light. The fluid in which these marine animals lived at 

 remote periods must have been pure and transparent to allow the 

 passage of light to organs of vision resembling those of livino- Cru- 

 staceans ; and this train of reasoning naturally leads us still further, 

 and to more important consequences, when we reflect on the general 

 adoption of the undulatory theory of light, and the connexion be- 

 tween light, heat, electricity, and magnetism. 



1 have heard it objected, that the zoologist and botanist had 

 already advanced such abundant proofs of' design in the construc- 

 tion of living animals, and plants, that the auxiliary evidence of 

 palaeontology was useless, and that to appeal to fossils in support of 

 the same views was to add weaker to stronger arguments. In 

 the living animal, it is said, we can study its entire orcranization, 

 observe its habits, see the manner in which it applies each oro-an, 

 and so verify with certainty the ends for which any particular mem- 

 ber was formed and fashioned. But in the case of the fossil, we 



