Eggs also form good examples of the wonderful strength obtained by this principle, their thin shells protecting the yolk and the white, as well as the chick through its progress to maturity.
The last subject in this chapter is a curious example of an evidently accidental resemblance in form.
The figure on the right of the accompanying illustration will at once be recognised as one of those Salad-dressing Bottles which try to conceal by their shape the small volume of their contents.
That on the left represents one of the many forms through which the Medusa passes before it attains its perfect form. It was long thought to be a separate creature, and was known under the scientific name of Strobila. Modern researches have, however, made the discovery that it is one of the transitional stages between the creature known as the Trumpet-hydra (Hydra tuba) and the Medusa, popularly known as Jelly-fish.
The former almost exactly resembles the Hydra of our fresh waters. It is a tiny transparent gelatinous bag—so transparent as to be scarcely perceptible, and with some thirty or forty long and delicate tentacles hanging from its open end. These tentacles are used in catching the minute creatures on which it feeds. It is fixed, and, to use Mr. Rymer Jones’s simile, looks like a beautiful silk-like pencil waving amidst the water. Its length is not quite half an inch.
That it should be identical with the remarkable form shown in the illustration seems impossible, but such is the case. Its body becomes contracted as if tied with strings, and every segment thus formed develops a set of tentacles, breaks away, and swims off in the form of a Medusa. The upper segment is exhibited as undergoing this process.
The figure is magnified so as to show the structure better, its right length being about one-third of an inch. A full and graphic history of this creature and its manifold changes may be found in Mr. Rymer Jones’s “Aquarian Naturalist.”
It is not likely that the inventor of the Salad-dressing Bottle ever saw a Hydra, but the resemblance is strangely exact.