PEEPS INTO NATURE'S NURSERIES.
I.—THE LIFE-HISTORY OF THE COMMON FROG.
How is it that people as a rule have such a dislike for frogs? Many people, even those who live in the country, credit them with the power of spitting poison, and even those who do not share this belief, regard them as creatures to be shunned. Perhaps this short outline of the life-history of these poor creatures, so unjustly 'sent to Coventry,' may gain for them at least a favourable hearing. Frogs make most charming pets, and I am never without a few on my study table. From their lives these facts are taken.
Let us begin from the very beginning—the hatching out of the eggs. Frogs' eggs and birds' eggs are really not so unlike as they seem at first sight, for though the frog's eggs have no shell, yet, just as in the bird's egg, there are two essential parts to be distinguished—the formative material out of which the young frog grows and the yolk on which the growing animal feeds. By the untrained eye nothing more can be seen in the frog's egg than a small black ball enclosed within a clear jelly-like substance. At the time the egg is laid this outer jelly is hardly noticeable, but it soon swells up, and thus forms a soft, elastic covering to the growing frog, effectually protecting it from injury. This black ball, by the way, answers to the yellow yolk of the hen's egg: it differs from the yellow yolk in that it is colourless internally, and black externally. The black outside coat apparently serves to attract the heat of the sun, and thereby to bring about the hatching process, which the hen does by the warmth of her own body.
Fig. 1.—A to G: Stages in the growth of the Tadpole, greatly magnified.
These eggs are furthermore remarkable in that they are laid, not one by one, as a hen lays, but in thousands, and in water, forming an enormous speckled mass. Take a portion of such a mass and watch it. Day by day you will see the black spot gradually assume a distinct shape (fig. 1, A): a little later a head and tail can be made out.
Fig. 2.—Mouth of Tadpole,
greatly magnified.
