244 ENTOMOLOGY. 



of the shell is extended by the application of fresh 

 layers of the shelly matter to the margin, and its 

 thickness is increased by a coating on the inner sur- 

 face. 



Shell is hardened by carbonate of lime, bone by 

 phosphate of lime. 



Crabs. 



Crabs have the power of parting with their claws 

 by a voluntary effort, and have also the power of re- 

 producing the whole limb ; but, apparently, no pro- 

 vision has been made for the repair of injured parts, 

 except by rejecting the whole claw, and having a 

 totally new one produced. 



The Nautilus. 



The shell of the nautilus is formed of a number of 

 chambers, the partitions of which are pierced through. 

 The animal resides in the largest and last-formed 

 chamber, and from it an elastic tube passes through 

 the pierced septa, or divisions, and terminates in the 

 first. With this tube it is supposed to exclude or 

 admit the water, and thus raise or depress itself in 

 the ocean at pleasure.* 



The back of the nautilus-shell resembles a canoe ; 

 on this it throws itself, with two feet raised in the air, 

 spreading over them a thin membrane for a sail, and 

 paddling like oars with the other two feet. 



The Polypus. 



The polypus and puceron are singularly mis-named, 

 for the first has no feet at all, and the second, so far 



* The Nautilus family claims the very highest antiquity, be- 

 ing equally found in rocks of the oldest and newest formations, 

 and having survived uninjured the debacles of half a dozen 

 worlds. It might consequently be engrafted on coats of arras, 

 as emblematic of the most extreme and indisputable antiquity. 



