72 INTRODUCTION TO ZOOLOGY. 



hearing from them expressions of . the most unfeigned delight. 

 Let the reader try the experiment. Go at low water to a 

 rock on the beach, choose a few of the oldest and largest 

 Limpets, left uncovered by the receding tide, and encrusted 

 with the Acorn-shells. As the enclosed animals have then 

 been without nourishment for two or three hours, they will 

 be quite ready for another meal. Throw the Limpet-shells 

 into the glass of sea-water, and in a 

 minute or two the Acorn-shells upon 

 them will begin to open. Presently a 

 beautiful feathered apparatus (Balanus, 

 Fig. 46) will be extended, then with- 

 drawn. It will again be put forth, and 

 again retracted; but with such grace, 

 regularity, and precision, that the eye 

 regards it "with ever new delight." 

 And when the same exquisite mecha- 

 nism is exhibited by every one of them, 

 either in succession or simultaneously, 

 and when we consider that it thus minis- 

 ters, at the same moment, both to respiration and nutrition, a 

 train of ideas is excited, which rises from the humble shell to 

 HIM by whom it has thus wondrously been fashioned. 



CLASS III CRUSTACEA. 

 CRABS, LOBSTERS, SHRIMPS, &c. 



" What is man, 



If his chief good, and market of his time, 



Be but to sleep and feed ? A beast no more. 



Sure He that made us with such large discourse, 



Looking before and after, gave us not 



That capability and godlike reason 



To fust in us unused." SHAKSPEAIIE. 



"THE name of this class," says Professor Owen, "refers to 

 the modification of the external tegument by which it acquires 

 due hardness for protecting the rock-dwelling marine species 

 from the concussion of the surrounding elements, from tho 

 attacks of enemies, and likewise for forming the levers and 

 points of resistance in the act of supporting the body, and 



