402 



Insect Architectur 



after the gall-fly has made a puncture and pushed her 

 egg into the hole, we may suppose that she covers it 

 over with some adhesive gluten or gum, or the egg itself, 

 as is usual among moths, &c., may be coated over with 

 such a gluten. In either of these two cases, the gluten 

 will prevent the sap that flows through the puncture from 

 being scattered over the leaf and wasted ; and the sap, being 

 thus confined to the space occupied by the eggs, will ex- 

 pand and force outwards the pellicle of gluten that confines 



Bedeguar Gall of the Rose, produced by Cynips I-OSCR. 



it, till becoming thickened by evaporation and exposure to 

 the air, it at length shuts up the puncture, stops the further 

 escape of the sap, and the process is completed. This 

 explanation will completely account for the globular form of 

 the galls alluded to ; that is, supposing the egg of the gall- 

 fly to be globular, and covered or coated with a pellicle of 

 gluten of uniform thickness, and consequently opposing uni- 

 , form resistance, or rather uniform expansibility, to the sap 

 pressing from within. It will also account for the remark- 



