334 



INSECT LIFE. 



seeds are planted or small plants set. The width of 

 the space between the plates of glass depends on the 

 width of two strips of wood placed between them, 



one at each end, and should 

 be only wide enough to allow 

 the insects under observation 

 to move freely through the 

 soil. If it is too wide the in- 

 sects will be able to conceal 

 themselves. Immediately 



outside of each glass there is 

 a piece of blackened zinc, 

 which slips into grooves in 

 the ends of the cage, and 

 which can be easily removed 

 when it is desired to observe 

 the insects in the soil. Fig. 

 294 represents a small section 

 of such a cage with the zinc 

 removed. 



In a more expensive form 

 of the cage, which is used in 

 the Insectary of Cornell Uni- 

 versity (Fig. 295), there is 

 only one plate of glass next 

 to the soil, the place of the 

 other plate of glass being oc- 

 cupied by a porous tile, be- 

 tween which and an outer 

 plate of glass is packed a lay- 

 er of moss. By wetting the moss sufficient moisture 

 passes through the porous tile to keep the soil in 

 good condition for the growth of the plants in the 



F13. 296. 



-A sectional view of a 

 root cage. 



