74 MECHANICAL FUNCTIONS. 



Fig. 59. Fig. 59 representsts another of 



these geniuses enveloped in a riband, 



^^M^--O=/~^B^ mac ^ e f P ieces f leaves joined to- 

 ^^BiimtfiMSp> gether, and rolled on like a bandage, 

 the folds being laid with as much 

 regard to symmetry and skill, as the neatest surgeon 

 displays in dressing a limb. 



Sometimes these mantles are constructed with small 

 Fig. 60. shells cemented together, as seen by 



Fig. 60. These shells are commonly 

 empty, but it seems the builder does 

 not always wait for this, sometimes 

 k employing living snails, when their 

 sizes happen to suit his wants. 



It appears that this insect, when out of its case, can 

 do little more than crawl along the bottom of the brook, 

 where it lives. But when clothed in the manner rep- 

 resented, it floats along near the surface, or sinks towards 

 the bottom at pleasure ; generally retaining the perpen- 

 dicular position, but changing it to the horizontal, or 

 turning the head downwards, at will. These different 

 positions, as well as some motion in any direction, the 

 insect gains by using its feet as paddles, these parts being 

 always out of the case and free. 



But the most wonderful point in this history is the 

 judgment involved in the selection of materials, which 

 when united to the body of the insect will exactly coun- 

 terpoise the whole, so that it neither rises to the surface, 

 nor sinks to the bottom, but may be made to do either 

 by the small degree of force exerted by the feet. 



A vast number of instances might be selected of the 

 ingenuity, craft, and seeming discretion of the Insect 

 tribes, especially of the bee, ant, spider, and wasp, but 

 for these, we must refer the reader. to works on Ento- 

 mology. 



What is said to bo the most wonderful point in the history of th 

 caddis worm ? 



