EFFECTS OF CHANGES IN TIIE COSMICAL ENVI RONMENT OF TILE GENESIS OF LIFE-FORMS. When the earth was cooling down from a gaseous to a solid condition, it is most probable that the changes in the cosmical environment had an im mediate and creative or modifying effect on the beginnings of life. It is certain that the action of the same cosmical agents, such as motion, gravity. electricity, etc., width have determined the spherical shape of the planets. as well as of a drop of water, has been concerned in determining the shapes of cells. of eggs. of the simplest organ isms. and is the basis of all physiological phe nomena, as well as of motion in animals.
Plant and animal life arc' influenced in a way we do not understand by electricity; they are also influenced by variations in the pressure of the air. Jaeger claims that the force of gravitation is the primitive morphogenetie factor in the develop ment of animals. In the growth of plants the influence of gravity and light is marked. The iiillifence of gravity on the form of shells is no ticeable. To this has been, by Hyatt, attributed
the asymmetry of univalve shells.
The mechanical state of the medium is impor tant in modifying the shape of animals. The spindle-shaped body of fishes enables them to cleave the water; so it is with the shapes of winged animals, whether insects, birds, or ptero dactyls. When some terrestrial mammal was driven by necessity or competition with its fel lows to seek a livelihood in the sea, and thus gave origin to the order of whales, its body un derwent a transformation; it became fish-like in shape, and while from disuse it lost its hind limbs, the fore legs were converted into fins.
When animals of very different types, such as the earthworm, many sea-worms. multitudes of parasitic worms, the boring larvae of insects, live in a denser medium than water, and have been obliged to burrow in the soil, or in the dense tis sues of their hosts, the body tends to become elongated, cylindrical, and pointed at each end.