INSECTS. 223 



the aniina'i, whereby it avails itself of its gift, and of the con- 

 stitution of its glands — to say nothing of the work being 

 commenced before the animal is born — are things which 

 can, with no probability, be referred to any other cause 

 than to express design ; and that not on the part of the ani- 

 mal alone — in w^iich design, though it might build the house, 

 it could not have supplied the material. The will of the 

 animal could not determine the quality of the excretion. 

 Add to which, that the shell of the snail, with its pillar and 

 convolution, is a very artificial fabric ; while a snail, as it 

 should seem, is the most numb and unprovided of all arti- 

 ficers. In the midst of variety, there is likewise a regularity 

 which could hardly be expected. In the same species of 

 snail, the number of turns is usually, if not always, the same. 

 The sealing up of the mouth of 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 sJiells, particularly to those of the uni- 

 valve 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 giveii, art 

 can produce so strong a case as are some of these shells ; 

 which defensive strength suits well with the life of an ani- 

 mal 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 excre- 

 tion, not only of congealing, but of congealing — or, as a builder 

 would call it, setting — in water, and into a cretaceous sub- 

 stance, firm and hard. This property is much more extra- 

 ordinary, and, chemically speakmg, more specific, than that 

 of hardening in the air, which may be reckoned a kind c 

 exsiccation, like the drying of clay into bricks. 



Ill In the bivalve order of shell-fish, cockles, miscius, 

 oysters, etc., what contrivance can be so simple or so clear 

 AS the insertion, at the back, of a tough tendinous substance. 



