74 Wisconsin Academy of Sciences, Arts and Letters . 
in doing this is a mystery.” In a letter to F. M. Webster, 
published in Insect Life (10), E. M. Pritchard writes:—‘T 
found a small number settled on the leaves and limbs of the 
ash and willows, where they seem to be feeding on the sap. 
Today I have been watching them more carefully and find 
that they cut a rough gash almost completely around the limb, 
seeming to kill the outer bark as far as they cut.” Webster, 
at the end of the paper, adds:—-“It seems quite possible that 
they gnaw the bark for the purpose of feeding upon the sap, 
as intimated by Mr. Pritchard, yet this does not appear to be 
fully proven. In other words, it would as yet be too much 
to say that in cutting the incisions the insect has no object in 
view other than that of obtaining food.” While observing a 
number of saw-flies in the act of cutting incisions, we chanced 
to come across a twig from which sap was oozing from a 
freshly cut wound. About half a foot below the wound a fe¬ 
male saw-fly was started up the twig. While she was walking 
slowly up the branch, w r e noticed that the palps were contin 
ually in motion. When the insect came to the sap, she sud¬ 
denly stopped and began to feed upon the liquid. While work¬ 
ing on the anatomy and histology of the alimentary canal, "we 
often noticed bits of bark in the lumen of the crop. Some of 
the specimens which were dissected had the crop filled with a 
clear liquid. Undoubtedly the only object which the saw-fly 
has in view in making the incisions is to tap the fibro-vascular 
bundles and thus secure its nourishment. 
If one examines the leaves shortly after the eggs have 
hatched, one often notices rusty spots on the upper and lower 
sides of the leaf. Frequently, however, these rusty spots are 
■entirely absent in those leaves wherein eggs had been deposited. 
Then, again, one may find, especially on those where the egg 
for some reason or other failed to hatch, a dense fungous 
growth within the receptacle. 
