American Toad — Part 3

Bufo americanus Le Conte

The American toads are in the ponds from late April until July. They may appear much earlier if the spring is early. The males--who alone do the singing--are the first arrivals. During a large part of these months they sing both day and night. If the season is unduly cold, they may be silent for days or weeks together, reappearing on the return of a higher temperature.

The eggs which are laid (April 14, 1890; April 6, 1891. Baltimore, Md. T. H. Morgan. Bufo americanus breeds in April and May, sometimes in July. C. F. Hodge, Worcester, Mass.) in long curling masses, (likely to be tangled among the waterweeds and stretched from object to object in secluded, shallow parts of the pond), are black above and white underneath. They are arranged in a single row, in a transparent jelly-like mass cylindrical in shape, and are fertilised in the water as they are laid. The toads may be removed from the pond to an artificial one, and the eggs will be laid as though there had been no disturbance.

The jelly-like substance about the eggs is scarcely visible when the eggs are first laid, but it swells in contact with the water until it becomes very conspicuous. Perfectly clean and transparent in the beginning, it soon becomes discoloured by the sediment of the water until one may look directly at coils of the eggs and not see them, because of their resemblance to debris at the bottom of the pond.

The eggs are small (less than 1 1/2 mm. in diameter). Their number is incredibly high. Various layings counted have yielded between four and twelve thousand eggs each. If the eggs are laid early, the development is comparatively slow. But if the eggs are laid later, when the temperature is more steadily high, or if they are kept in the warm atmosphere of the house, the development is remarkably rapid.

Those figured here were laid Friday, June 12, 1903, indoors. They were photographed on Saturday, twenty-four hours later, when they were very much increased in size and all the fertilised eggs were entirely black.

Monday they were photographed again. The jelly-mass is now much less solid; the coils are straightening, but still hold their cylindrical shape. The eggs are no longer eggs, but young tadpoles in which head and tail are easily distinguished. What is our surprise twenty-four hours later--just four days from the time of laying--to find the tadpoles out of the jelly-mass clinging to its outer surface or to nearby waterweeds. The rounded head is uppermost, the tail with its thin fin hangs downward. At the place where we should expect the mouth to be, there are two small black elevations, called suckers. These secrete a sticky substance by means of which the young tadpoles attach themselves to weeds or grasses. The jelly-mass is now almost wholly disintegrated and the unfertilised eggs are very conspicuous swollen gray-and-white objects. These are masses of foul matter, which should be removed if the tadpoles are developing in a small amount of water under artificial conditions.

By Thursday the head, body, and tail are still more clearly differentiated one from another, and finger-like extensions from the neck are conspicuous when the tadpole is viewed from above or below. These are the gills for breathing; they have been present fully forty-eight hours, but were so small and delicate that they were very difficult to see. Ever since the tadpoles emerged from the jelly-mass (which has now totally disappeared). they have moved with a vigorous wiggling of the tail whenever disturbed. Now they are becoming more active and start off on short circuitous voyages when there seems to be no visible disturbance.

On Friday, when they are a week old, their activity is still greater. The head is apparently much larger, but the gills are less conspicuous than before and seem to be farther back on the neck. The fact is, a membrane is growing backward from the anterior part of the head. This membrane will eventually cover the gills and the neck region, making the tadpole look as though it consisted of a large head and a tail, but no body, because head and body become so thoroughly blended. (For details of the development, see Leopard Frog, pp. 176 to 181.).

On Saturday they are still clinging quietly, except for occasional sallies to neighbouring weeds by very circling routes. The gills are wholly covered, except for two minute finger-like ends on the left side.