THE POPULAR SCIENCE MONTHLY.
of one segment, or cell, type of both the cœlenterata and molluscoida of Mr. Huxley, and of all mono-segmental creatures.
Henceforward, this type is the unit of animal organisms, as a simple cell is the unit of primary vegetal life. For want of a better term such a creature may be called a mono-segmentary, consisting of but one segment or unit; while all others are polysegmentarian—consisting of more sections than one.
Nature retains her habits very tenaciously. If we have seen her rising to higher and higher types of vegetal structure by adding cell to cell; duplicating cells by division and holding on to them by adhesion; extending them by increase upon one axis into a baculus; upon two axes into thalli; and folding them again into fronds, leaves, and fruit we no less see her handling this new unit of organization in a similar manner. Ay! the parsimonious builder again goes through precisely the same means of progress. She works by compounding; by multiplication of segments; by gemmation; by the evolution of higher types; by a failure to expel the simple segments; until, by adhesions in fœtal life, a more complex creature is formed of multiplied powers.
Here, again, we come to great gulfs and faults in the strata, which naturalists tell us cannot be bridged over. There remain still the three highest types of organic creatures to be accounted for, namely, the annulosa, or articulata the mollusca, and the vertebrata. Our most eminent recent naturalists regard all these as unconnected with preceding forms, and unconnected with one another. Some of the very recent, as Haeckel, endeavor to show a consistent chain here by connecting directly molluscoids with vertebrates; dropping out of the series entirely the two great classes of mollusca and articulata, and leaving their evolution unaccounted for. True, there can be no objection to leaving them out of the chain, if they have no place in it. If we can arrive at vertebrates and man directly from the holothurius, well and good. It would be analogous to other proceedings of Nature, as in the separate evolution of the whole grand vegetal kingdom from the first living germs, in a direction exactly opposite, as it were, to animal evolution. But we should also account for the genesis of the two eccentric classes, and connect them in some way with primordial types.
|COLOR IN ANIMALS.|
THE variety of coloring in animal life is one of the marvels of Nature, only now beginning to be studied scientifically. It is vain to say that an animal is beautiful, either in symmetry or diversity of color, in order to please the human eye. Fishes in the depth of the Indian seas, where no human eye can see them, possess the most gorgeous tints. One thing is remarkable: birds, fishes, and insects, alone possess