Page:Popular Science Monthly Volume 31.djvu/833

Rh chances for destruction of the summer eggs in the dry and often dusty-soil are so numerous that only the most prolific species can maintain themselves under such conditions.

"Further, the marshes and shallower lakes are the favorite breeding-grounds of fishes, which migrate to them in spawning-time, if possible, and it is from the entomostraca found here that most young fishes get their earliest food-supplies—a danger from which the deep-water species are measurably free. Not only is a high reproductive power therefore rendered unnecessary among the latter by their freedom from many dangers to which the shallow-water species are exposed, but in view of the relatively small amount of food available for them, a high rate of multiplication would be a positive injury, and could result only in wholesale starvation."

The effect of birds on insect-life has engaged the attention of the same author. His inquiry was to ascertain whether birds originated any oscillations in the numerical proportion of insects upon which they feed. Many interesting facts are given which space forbids quoting.

A number of contributions have been made on the influence of environment and on geographical variation, to some of which reference must be made. Prof essor Alpheus Hyatt bears unequivocal testimony to the derivative theory, and recognizes clearly the influence of external surroundings in a memoir on the cephalopods, when in stating the law of organic equivalence he says: "The action of physical changes takes effect upon the irritable organism, which necessarily responds to external stimulants by an internal reaction or effort. This action from within upon the parts of the organism modifies their hereditary forms by the production of new growths or changes which are, therefore, adapted to the conditions of the habitat or the physical agents and forces from which they directly or indirectly originate"; or, slightly changing this interpretation in accordance with the same facts, each individual is more or less susceptible to the action of physical influences and those which respond most quickly to these influences, come more promptly in harmony with their environment, which is natural selection pure and simple.

Mr. Charles Morris, in a series of papers on "Organic Physics" and the "Polar Organization of Animals," presents many new and suggestive thoughts on the physico-chemical action in life and development. He concludes that "there are inherent in the germ energies and tendencies, chemical, molecular, or whatever we choose to call them, adapted to the complete unfoldment of the typical form. But, as appears evident, their operation can be checked by influences from external nature. There is a struggle between these contact influences and the innate organic tendencies."