It must be put to the credit of amphibians that they have made many
experiments in methods of parental care, as if they were feeling their
way to new devices. A common frog lays her clumps of eggs in the cradle
of the water, sometimes far over a thousand together; the toad winds two
long strings round and between water-weeds; and in both cases that is
all. There is no parental care, and the prolific multiplication covers
the enormous infantile mortality. This is the spawning solution of the
problem of securing the continuance of the race. But there is another
solution, that of parental care associated with an economical reduction
of the number of eggs. Thus the male of the Nurse-Frog (Alytes), not
uncommon on the Continent, fixes a string of twenty to fifty eggs to the
upper part of his hind-legs, and retires to his hole, only coming out at
night to get some food and to keep up the moisture about the eggs. In
three weeks, when the tadpoles are ready to come out, he plunges into
the pond and is freed from his living burden and his family cares. In
the case of the thoroughly aquatic Surinam Toad (Pipa), the male helps
to press the eggs, perhaps a hundred in number, on to the back of the
female, where each sinks into a pocket of skin with a little lid. By and
by fully formed young toads jump out of the pockets.
In the South American tree-frogs called Nototrema there is a pouch on
the back of the female in which the eggs develop, and it is interesting
to find that in some species what come out are ordinary tadpoles, while
in other species the young emerge as miniatures of their parents.
Strangest of all, perhaps, is the case of Darwin's Frog (Rhinoderma of
Chili), where the young, about ten to fifteen in number, develop in the
male's croaking-sacs, which become in consequence enormously distended.
Eventually the strange spectacle is seen of miniature frogs jumping out
of their father's mouth. Needless to say we are not citing these methods
of parental care as examples of intelligence; but perhaps they correct
the impression of amphibians as a rather humdrum race. Whatever be the
mental aspect of the facts, there has certainly been some kind of
experimenting, and the increase of parental care, so marked in many
amphibians, with associated reduction of the number of offspring is a
finger-post on the path of progress.
§ 4