THE WESTERN GRASS-STEM SAWFLY. 21 
the dorsal part of the pygidium being used as a fulcrum to extract 
them. They are inserted again, this time often with a twisting mo- 
tion as if trying to enlarge the opening. They are finally forced in 
as far as possible, as is evidenced by the tenseness of the rear legs 
straining at the stem, and are held in this position for half a minute or 
more. This is probably when the egg is deposited, the insect standing 
practically motionless except for a slight vibration of the antennas . 
A laboratory note may be of interest, giving in detail some of the 
facts that have been mentioned above : 
June 5, 1912. The adult Cephus were emerging freely from the Elymus material 
brought from the mountains, and it occurred to me it might be possible to secure some 
views with the camera if they could be induced to oviposit. Several females were ob- 
served attempting opposition in the dry stems from which they had recently emerged. 
A green stem of Elymus was planted in a tumbler of wet sand and the camera 
focussed on this stem about midway. After a few trials I discovered that this stem 
must be short and headless. 
The females were taken from the cage and placed, one at a time, on the damp sand 
in the tumbler . Their first act in every case was to spend a long while drinking eagerly 
of the water held in suspension by the sand. A few of them sipped water for as much 
as halfan hour before they could be induced to leave. When guided to the base of the 
Elymus stem they would usually ascend without a moment's hesitation. Once started 
they would go to the very top and there would either preen themselves interminably, 
or would wheel and descend with the usual cautious, hesitating gait, a few steps at a 
time. When part way down, without apparently choosing any especially suitable 
spot, the abdomen would arch and opposition would begin. Sometimes these efforts 
were plainly failures, but some of the flies would sink their saws well into the tissue of 
the stem and stand for a number of seconds motionless, thus affording an opportunity 
for the camera. 
Much time was lost to-day because of the exasperating neatness of these insects. 
Each one would brush herself over and over again with the most minute exactness and 
no amount of urging would avail to shorten the process. The same careful preening 
has been frequently observed also in the field. 
Several life-size views of these flies were obtained to-day by the above method, views 
that would be impossible in the field because of the almost constant motion of the 
limber grass stems. Several of the females became confused to-day when compelled to 
remain on a certain part of the grass stem during oviposition, and faced up the stem 
instead of down as they invariably do, normally. 
When busy with oviposition they seem oblivious to whatever is 
going on around them, and the writer has repeatedly watched, through 
a half-inch triplet, the female manipulating her saws. Close observa- 
tion did not annoy her in the least when the lens was carefully handled, 
and she paid no attention to the proximity of the onlooker. Under 
the closest scrutiny it is impossible to determine just when the egg is 
passed into the stem. It is probably at the time when the female 
stands motionless after the saws have been driven in to their full 
length. 
The function of these saws appears to be twofold. At Pinto, Utah, 
in June, 1912, the writer found that the eggs were invariably placed 
