One is often guided to the right place by noticing the direction from which the song or call of the toad comes. The call of the toad is more or less like that of the tree toads. In general it sounds like whistling, and at the same time pronouncing deep in the throat, bu-rr-r-r-r-. If one watches a toad while it makes its call, one can soon learn to distinguish the sound from others somewhat similar. It will be found that different toads have slightly different voices, and the same one can vary the tone considerably, so that it is not so easy after all to distinguish the many batrachian solos and choruses on a spring or summer evening. It will be noticed that the toad does not open its mouth when it sings, but, instead, the resonator or vocal sac under its mouth and throat is greatly expanded. One must be careful to distinguish the expansion of the mouth in breathing from the expansion of the vocal sac. See the left hand toad in the drawing (Fig. 111) for the vocal sac, and the toad in hibernation (Fig. 121) for the expansion of the mouth in breathing. It is only the males that possess the vocal sac, so that the toad chorus is composed solely of male voices. The eggs are laid in long strings or ropes which are nearly always tangled and wound round the water plants or sticks on the bottom of the pond. If the pond is large and deep, the eggs are laid near the shore where the water is shallow. If the eggs have been freshly laid in clear water the egg ropes will look like glass tubes containing a string of jet black beads. After a rain the eggs are obscured by the fine mud that settles on the transparent jelly surrounding them, but the jelly is much more evident than in the freshly laid egg strings. Secure enough of the egg string to include 50 or 100 eggs and place it in a glass fruit dish or a basin with clean water from the pond where the eggs were found. Let the children look at the eggs very carefully and note the color and the exact shape. Let them see whether the color is the same on all sides. If the eggs are newly laid they will be nearly perfect spheres. [Illustration: _Fig. 111. The toad in various stages of development from the egg to the adult_] Frogs, salamanders and tree toads lay their eggs in the same places and at about the same time as the toad we are to study. Only the toad lays its eggs in strings, so one can be sure he has the right kind. The others lay their eggs in bunches or singly on the plants, so they never need be mistaken for the ones sought. [Illustration: _Fig. 112. Just hatched toad tadpoles climbing up where the water is better aerated._] The eggs which are taken to the school house for study should be kept in a light place; an east, south or west window is best.