accomplishment, would naturally result at last in the production of a race of animals in which, as in the frogs of to-day, the power of changing colour is universal. Fig. 217.—Head of Male Edible Frog, seen from the left side, showing inflated vocal sacs. (× 1.) The laying of the eggs.—About the end of March the frogs resort in great numbers to shallow ponds and ditches, pair with much croaking, and the females lay their eggs or “spawn.” Both sexes croak, and the male of the edible frog, though not of the common grass frog, is able to make more noise in virtue of a pair of vocal sacs (Fig. 217), which he can inflate with air from the mouth (Fig. 216), and which act as resonators. After spawning, the frogs leave the water, abandoning the eggs to their fate, and resume their ordinary terrestrial life, until approaching winter prompts them to hide in the mud and go to sleep. [Pg 340] 61. THE DEVELOPMENT OF THE FROG. 1. A simple aquarium.—A simple aquarium, in which the development of the frog from the egg may be watched, is easily made. Obtain a fairly large basin, and cover the bottom with sand, mud, and stones from a pond. Arrange these so that the bottom shall shelve from the surface of the water at one side to a depth of 3” or 4” at the other. Put in some stones covered with green slime, which will almost certainly be found in the pond, plant a few water-weeds, and allow the water to clear. 2. Frog spawn.—Having prepared the aquarium, obtain, towards the end of March (or earlier in a mild spring) a handful of frog spawn from a pond or ditch. It forms a mass of jelly in which the true eggs—small balls about ¹/₁₀” in diameter—are imbedded. Put this in the aquarium and examine it carefully every day, making the observations described below. If possible, obtain a pair of spawning frogs, and place them in a bucket with a little water, so that the earliest stages also may be studied. 3. The eggs before hatching.—Observe the globe of jelly which surrounds each egg. Try to pick it up between your finger and thumb. Do you think it is of any use in protecting the eggs from being eaten by fishes, birds, etc.? Remove the jelly as completely as possible from one egg, put the egg in a watch-glass with a little water, and examine it carefully with a strong lens. To which of the stages shown in Fig. 218 does it correspond? If possible, treat a newly-laid egg in the same manner and examine it every hour or so through the day. Make notes of the time elapsing between the various stages shown in Fig. 218.