By William Spence, Esq. 



27 



calculated upon. Not only were they more than usually 

 abundant near the margins of all the old cankers, but I ob- 

 served their masses of excrement adhering, in every direction, 

 to the surface of the healthiest Pear and Apple-trees in the 

 garden ; and wherever these indications appeared, the appli- 

 cation of the knife always detected the caterpillar beneath. 



It is thus evident that where they abound, no other cause 

 is wanting to generate canker and disease. Though their 

 attacks upon the bark and alburnum should not at first be 

 extensively injurious, the admission of water into their empty 

 cells, and frequent repetitions of the mischief, must, in the 

 end cause rottenness; and it is perhaps not improbable 

 that to these insects should be often primarily attributed 

 the canker laid to the charge of the soil, or the mode of 

 cultivation. 



After these prefatory remarks, I shall proceed to describe 

 the insect in its different states, adding such observations as 

 have occurred to me upon its economy, and the most proba- 

 ble means of extirpating it. 



Eggs. I have never been able to detect any of these upon 

 the parts of the tree where I conjecture they are laid ; but 

 several were deposited on the sides of a glass jar, under 

 which I had kept the two sexes from their first exclusion. 

 They are lentiform, flat below, slightly convex above, smooth, 

 pale red in the middle, with a white and apparently mem- 

 braneous margin. Altogether they very much resemble the 

 seeds of the common garden Stock, except that they are not 

 above one-fourth of the size ; and they presented an ap- 

 pearance so very dissimilar to that of the eggs of insects in 

 general, that I for some time overlooked them. 



