Fig. 4.—Entire fluid filled with bubbles, and the froth thus made enveloping the stem.
Magnified Figures of Aphrophora, showing Successive Stages in the Production of Froth.
Let one provide himself with a good hand lens, a bit of glass (a watch crystal is especially suitable for this purpose), and a common camel’s-hair brush, and he is ready to make a preliminary study of Aphrophora. The brush is convenient for easily removing the insect from the froth which invests it. If the insect is cleared from the mass of froth, it will crawl quite rapidly along the stem of the plant, stopping at times to pierce the stem for the purpose of sucking the juices within, and finally settling down in earnest, evidently exerting some force in thrusting its piercing apparatus through the outer layers, as shown by the firm way in which it clutches the stem with its legs. After sucking for some time, a clear fluid is seen to slowly exude from the posterior end of the abdomen, flowing over the body first and gradually filling up the spaces between the legs and the lower part of the body and the stem upon which it rests ([Fig. 2]). During all this time not a trace of an air bubble appears; simply a clear, slightly viscid fluid is exuded, and this is the only matter that escapes from the insect. In other words, its secretion of clear fluid is precisely like that of the Madagascar species referred to by Westwood and others.
This state of partial immersion continues for half an hour or more. During this time, and even when the insect is roaming up and down the grass or twig, the posterior segments of the abdomen are extended at intervals, the abdomen turning upward at the same time. It is a kind of reaching-up movement, but whether this action accompanies a discharge of fluid or is an attempt at reaching for air I have not ascertained. Suddenly the insect begins to make bubbles by turning its tail out of the fluid, opening the posterior segment, which appears like claspers, and grasping a moiety of air, then turning the tail down into the fluid and instantly allowing the inclosed air to escape ([Fig. 3]). These movements go on at the rate of seventy or eighty times a minute. At the outset the tail is moved alternately to the right and left in perfect rhythm, so that the bubbles are distributed on both sides of the body, and these are crowded toward the head till the entire fluid is filled with bubbles, and the froth thus made runs over the back and around the stem ([Fig. 4]).
Even when partially buried in these bubbles the tail is oscillated to the right and left, though when completely immersed the tail is only occasionally thrust out for air which is allowed to escape in the mass apparently without the right-and-left movement, though of this I am not sure. It is interesting to observe that in half a minute some thirty or forty bubbles are made in this way—a bulk of air two or three times exceeding the bulk of the body—without the slightest diminution in the size of the body.
If the insect is allowed to become dry, by resting it upon a piece of blotting paper, and is then placed upon a piece of glass and a drop of clear saliva be allowed to fall upon it, it proceeds to fill up this fluid with bubbles in precisely the same manner as it did with its own watery secretion. It is quite difficult to divest the creature of the bubbles of air which adhere to the spaces between the legs and the segments on the underside of the body. It may be readily done, however, by immersing it in clear water and manipulating it with a brush. If now it is again dried and placed on the glass it will slowly secrete what spare fluid it has in its body, but not the minutest bubble of air is seen to escape. These experiments should be made on glass, for then one may get transmitted light, and the highly refractive outlines of the air bubbles are more quickly detected. Using a higher power with a live cell, new features may be observed. Confining the insect in this way, inclosed in a drop of water, a very clear proof is offered that it gets all the air for its froth in the way I have described. So long as the insect remains surrounded by water not the minutest bubble of air is seen to escape from the body. During this immersion the creature is incessantly struggling to reach the edge of the drop, and no sooner has this been accomplished than it thrusts out its tail and begins the clutching of air and the making of bubbles. The bubbles, however, disappear as soon as made, as the clear water will not preserve them. As the water becomes slightly viscid from the insect’s own secretions, the bubbles remain for a longer time. A bubble will be partially released and then held, or even partially withdrawn, between the claspers.
Fig. 5.—Showing underside of posterior extremity of body with appearance of branchiæ.
Fig. 6.—A single branchia under slight pressure.