NATURAL FOOD. 35 



wich and Gravesend, they are very abundant. One of 

 the most surprising instances of their skill occurs in 

 the structures of which small stones are the principal 

 materials. The problem is to make a tube about the 

 width of the hollow of a wheat straw, or a crow quill, 

 and equally smooth and uniform. Now the materials 

 being small stones full of angles and irregularities, the 

 difficulty of performing this problem will appear to be 

 considerable, if not insurmountable: yet the little 

 architects, by patiently examining their stones, and 

 turning them over on every side, never fail to accom-. 

 plish their plans. In other instances, when the mate- 

 rials are found to possess too great specific gravity, a 

 bit of light wood, or a hollow straw, is added to buoy 

 up the case. The grubs themselves are admirably 

 adapted for their mode of Ufe, the portion of their 

 bodies which is always enclosed in the case, being soft 

 like a mealworm, or garden caterpillar, while the head 

 and shoulders, which are for the most part projected 

 beyond the door-way in search of food, are firm, hard, 

 and consequently less liable to injury than the protected 

 portion, should it chance to be exposed. These grubs 



-V; "f : '*t\&$b&$M&~, 



Figures of four caddis worms in variously formed cases. 

 D 2 



