PERIODICAL CICADA
surface. A good idea of the size and shape of these cham- bers may be obtained by filling the opened holes with a mixture of plaster of Paris in water, letting the plaster harden, and then digging up the casts. Figure I t5 shows castsofa number ofchambers madein this way. Some, it is seen, are mere cups about an inch in depth, but most of them are long and narrow, descending several inches into the ground, the longest being six inches or more in depth. The width is usually about five-eighths of an inch. All the chambers have a distinct enlargement at the bottom, and most of them are slightly widened at the top. The upper wall of each is separated from the surface by a laver of undisturbed soil about hall an inch in thick- ness, which is not broken until the insect is ready to enlerge. The shafts are seldom straight, their courses being more or less tortuous and inclined to the surface, as the miner had to avoid roots and stones obstructing the vertical path. The interior contains no débris of any kind, and the walls are smooth and compact. Below each chamber there is always evidence of a narrower burrow going irregularly downward into the earth, but this tunnel is filled to the chamber floor with black granu- lar earth. The burrows examined by the writer near Washington in ?9?9 were dug through compact red clay, and the lower tunnels here made a distinct black path through the red of the surrounding clay, where some could be followed for a considerable distance. The black color of the earth filling the tum?els was possibly due to an admixture of fecal matter. The chambers, as we have noted, are closed at the top until the cicada is ready to emerge. The largest chambers are many times the btilk of the nymph in volume, and it becomes, then, a question as to what the insect does with the material it removed in making a hole of such size. It seems improbable that it could have been carried down into the lower tunnel, for this would be filled with its own
[ ?891
INSECTS
