Page:Popular Science Monthly Volume 13.djvu/342

328 are of various and remarkable shapes, and are very interesting objects when seen under the microscope. They are the representatives of the calcareous plates which make up the hard shell of the sea-urchin.

Unlike as are the crinoid, brittle-stars, star-fishes, sea-urchins, and sea-cucumbers, in their form and general appearance, they are but different expressions of one and the same fundamental idea. They are all radiates, all possess calcareous plates—though these are at their minimum in the sea-cucumbers—and are covered with spines, tubercles, or a rough skin. They are all constructed according to a reigning number, the principal parts being in fives, or some multiple of five. If we imagine the sea-cucumber to be placed with its mouth downward and the tentacles to be replaced with teeth, the long body to be shortened upon itself so as to assume nearly the form of a hemisphere, and the microscopic calcareous particles to be enlarged so that they should touch one another, then we should have essentially the form and structure of the sea-urchin.

And if we imagine the sea-urchin with its segments spread out into a star-like form, instead of being brought near together, each perforated segment taking half of the imperforate one, and at the same time the spines to be reduced to tubercles and the plates to a network, then we should have essentially the form of a starfish.

Again, if the starfish had its body reduced to a well-defined disk, and its arms starting out abruptly from this disk, we should have all the most prominent features of the serpent-star.

And if the serpent-star had its mouth placed upward, its arms multiplied by branching, and its ab·oral region elongated into a stem, we should have the plant-like form of the crinoid.

And so it is in all parts of the material world. Nature has but comparatively few great types, but the forms included under these types are almost endlessly varied. Unity in diversity is a great law which prevails not only in the animal kingdom, but throughout the whole realm of Nature.



UTLINE —Even a qualified admission of the soundness of these views also compels the admission that the reconstruction of the principles of evidence is the crowning need of philosophy.

Such reconstruction will not be made on the base of Pyrrhonism, or the denial of the possibility of knowledge—for knowledge is possible,