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 oviposition 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 half an 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 oviposition 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 sec'onds 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 



