• 72 



THE CHAIN or LIFE. 



move up or down in the sea with the greatest facihty, using 

 its sucker-bearing arms and horny beak to seize and devour 

 the animals on which it preys. The buoyancy of the shell 

 seems exactly adapted to the weight of the animal ; and this 

 proportion is kept up by the addition of new air-chambers as 

 the body increases in size. In the modern seas this singular 

 little group stands entirely isolated, and its individuals are 

 so rare that it is difficult to procure perfect specimens for 



Vu:. 64.— Snuid (/,tf/4'w). Fi';. 65. -- Pearly Nautilii«fA/rt«///'<.9/(7w//7/«.v). 



/I, Mantle. />, Its dorsal fold, c, Hood. 

 o, Kyc. /, 'i'enlacles. _/, Funnel. ^, Air 

 chaiiilK-rs. //, ^>ii>liunclc. 



collections, though its mechanical structure and advantages 

 for the struggle for existence seem of the highest order. But 

 in the old world of past geological time the case was 

 altogether different. 



'J'he Nautiloid shell- fishes burst suddenly upon us in the 

 beginning of the Siluro-Cambrian, or Lower Silurian, Barrande's 

 second fauna; and this applies to all the countries where 



