No. 504] ORIGIN OF FROTH IN SPITTLE-INSECTS 787 



parallela was taken from the frothy mass and by means 

 of a camel's hair brush was thoroughly freed from every 

 particle of froth. The specimen was then placed upon a 

 dry twig. It soon inserted its beak in the plant and 

 gradually increased in size. It projected the tip of its 

 abdomen extensively and then retracted it. This opera- 

 tion it repeated several times. Suddenly a small drop of 

 a clear liquid appeared at the very tip of the abdomen, 

 coming distinctly out of the anal opening. Observations 

 made with a hand lens upon other parts of the body, es- 

 pecially in the region of the dorsum, failed to show any 

 fluid whatever. The small drop was soon joined by an- 

 other, and these in turn were followed by many others, 

 the whole mass of fluid passing down on the ventral side 

 of the body along the channel formed by the sternites 

 and the prolongations of the pleurites (Figs. 1 and 6). 

 Again, the fluid was noticed to be fairly oozing out of 

 the anal opening. After a quantity had accumulated 

 about the body of the insect, it was noticed that the last 

 pair of legs, sometimes also the second pair, would reach 

 out to the region of the seventh and eighth abdominal 

 segments, then rub against the body and against one an- 

 other as if in the process of mixing substances. After 

 the fluid had been well mixed and the surface had been 

 covered by it, it was next observed that the nymph moved 

 the tip of the abdomen out of the liquid, opening up the 

 pair of lateral appendages of the ninth abdominal somite, 

 which immediately closed again. Then with a downward 

 movement these parts were immersed in the liquid and 

 the appendages, upon being opened, released a particle of 

 air in the fluid. This operation was repeated many 

 times, with the result that the insect was soon covered 

 with air bubbles, which gave the characteristic covering 

 a froth-like appearance. It was noticed that by changing 

 the size of the air-grasping pocket, the insect is able to 

 make bubbles of any size. For that reason, the bubbles 

 in the smaller forms are always very much smaller than 

 those of the larger spittle insects. It is partly this feature 



