HY R. J. TILLYARD. 373 



water, were two females of Diphlebia ovipositing. I watched the 

 operation witli the greatest interest. Kneeling down on the rock, 

 and shading the reed from the sun with my hat, I was able to 

 place my eye just above the insects. They appeared to be 

 encased, as it were, in silver from head to tip, owing to the fact 

 that tliey were completely surrounded with air. The operation 

 of ovipositing was conducted fairly quickly, by raising the abdo- 

 men slightly, puncturing the reed with the ovipositor, and insert- 

 ing an egg. Each female made two or three punctures nearly in a 

 horizontal line; then, by contracting her abdomen, three or four 

 ■more about one-quarter of au inch above the others, and so on; 

 every now and then climbing higher up the reed. One female 

 was working on one side of the reed, the other on the other; and 

 one was about four inches above the other. I watched them for 

 about five minutes, during which time they must have laid close 

 on fifty eggs apiece. Then the upper female began to ascend the 

 reed rapidly, and crawled out on to my hand, perfectly dry, the 

 second one following half-a-minute later. I captured both and 

 papered them. At the time I was astounded at the apparently 

 large amount of air held by them under water, but a little reflec- 

 tion made me see how easily they contrived to do so. The long 

 thin wings, folded back along the abdomen, reach nearly to its 

 tip, and were so placed as to enclose between them a large amount 

 of air, which passed also beneath the abdomen, forming a perfect 

 sheath or covering. Between the head and prothorax also, on 

 each side, a large bubble of air was held, and this extended back- 

 wards along the thorax and forwards under the eyes, so that 

 practicall}^ the whole insect was protected from the water. 

 Probably also the amount of air was sufficient to make the 

 specific gravity of the insect about the same as that of water, and 

 hence to enable it to move up and down in the swiftly running 

 water with great facility. 



I carefully gathered the reed, and carried it home in water for 

 examination. I found each leaf full of punctures for a distance 

 of about four to six inches. Each puncture contained beneath it 

 a transparent egg about 1 mm. long. I cut off one portion of the 



