OF INSECTS. 193 



the shell by the snail, is also well calculated for its warmth 

 and security ; but the cerate is not of the same substance 

 with the shell. 



II. Much of what has been observed of snails belongs 

 to shell-Jish and their shells, particularly to those of the 

 univalve kind ; with the addition of two remarks. One 

 of which is upon the great strength and hardness of most 

 of these shells. I do not know, whether, the weight being 

 given, art can produce so strong a case as are some of these 

 shells. Which defensive strength suits well with the life 

 of an animal, that has often to sustain the dangers of a 

 stormy element and a rocky bottom, as well as the attacks 

 of voracious fish. The other remark is, upon the property 

 in the animal excretion, not only of congealing, but of con- 

 gealing, or, as a builder would call it, setting in water, and 

 into a cretaceous substance, firm and hard. This property 

 is much more extraordinary, and, chemically speaking, more 

 specific, than that of hardening in the air ; which may be 

 reckoned a kind of exsiccation, like the drying of clay into 

 bricks. 



III. In the bivalve order of shell-fish, cockles, muscles,, 

 oysters, &c. what contrivance can be so simple or so clear, 

 as the insertion, at the back, of a tough, tendinous sub- 

 stance, that becomes, at once, the ligament which binds 

 the two shells together, and the Jdnge upon which they 

 open and shut. 



IV. The shell of a lobster's tail, in its articulations and 

 overlappings, represents the jointed part of a coat of mail ; 

 or rather, which I believe to be the truth, a coat of mail is 

 an imitation of a lobster's shell. The same end is to be 

 answered by both ; the same properties, therefore, are re- 

 quired in both, namely, hardness and flexibility, a covering 

 which may guard the part without obstructing its motion. 

 For this double purpose, the art of man, expressly exercised 

 upon the subject, has not been able to devise any thing 

 better than what nature presents to his observation. Is not 

 this therefore mechanism, which the mechanic, having a 

 similar purpose in view, adopts? Is the structure of a coat 

 of mail to be referred to art? Is the same structure of the 

 lobster, conducing to the same use, to be referred to any 

 thing less than art ? 



Some, who may acknowledge the imitation, and assent 

 to the inference which we draw from it, in the instance be- 

 fore us, may be disposed, possibly, to ask, why such imita? 



