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Show THE SPANS OF LIFE. DIFFERENCES OF DURATION IN MEN AND ANIMALS. One of the Shortest I. that of the May Fly and One of the Longest the Elephant's Ele-phant's Among Insects the Period ol Adult Life Varies Greatly. Au essay cf Weismann, charming and profound and written before the obsession of a - logical theory had carried car-ried him into arid metaphysics, discussed dis-cussed the duration of life in men and animals. To many, perhaps to most, living things, death comes unexpectedly, unexpected-ly, with an ironical indifference to the period of the animal's life or to its business bus-iness of the moment The man may be preparing to be merry; the bird may be a-building, the butterfly not yet dry from the chrysalis, when they are f alln upon by blind mischance, by enemies intent ouly on dinner or by unthinking microbes. Confronted by such extrinsic accidents, men cry out after their kind, the poet attuning an ineffectual lamentation, lam-entation, the moralist preaching, the pagan urging tp the day of pleasure, but the naturalist must be dumb. His opportunity comes with the animals that avoid or escape colliding fates, and that yet after a fixed period run down like a clock. The seeds of deaths apparently appar-ently have been lying inert in the body and come to fatal maturity after a lapse of time that varies little among individuals indi-viduals of the same species, but that ia widely different among different kinds of animals. Threescore and ten Is the natural period of man's lifa The elephant will live 200 years, the honse but half a century. cen-tury. Singing birds and fowls and pheasants pheas-ants will live for nearly 20 years, but parrots, eagles, falcons and swana are known to survive their century. Some live through nearly two centuries. Queen ants and working ants may live for years. Sir John Lubbock kept a queen ant alivo for 18 years, during all which period she continued to lay fertile fer-tile eggs, but the males live only a few days. Queen bees live two or three years; workers and drones a few mouths, although indeed in one sense the death of the latter is unnatural, as the workers work-ers drive them away from the stores of food, bo that they perish of starvation. Among insects generally the period of adult life varies greatly. Many, like the May flies, dance in the sun only for a few hours; the sexes meet, the eggs are deposited and the creatures die before be-fore nightfall Many butterflies and moths are unprovided with feeding organs or-gans and live only a few hours, others for many days. Leaving out of count certain minor factors, like the time required for growing grow-ing to a larger size and the slower growth of animals that must waste time and energy in capturing living food, it is certain that there is an intimate connection con-nection all through the animal kingdom between the duration of life and the reproductive habits. Animals, in one sense, are like the bright and fragrant flowers of plants; since when their function is accomplished, when seeds are formed, they wither and perish. The business of the animal seems to be, not to live its own life, but to reproduce its own kind, and the term of life at its disposal is adjusted accurately to the special difficulties of this purpose. Weismann and Alfred Russel Wallace suggest that death comes as soon as possible pos-sible after the due number of successors has been produced, in order that each species may always be represented by A full tale of young and vigorous individuals. indivi-duals. Natural selection acts like a contractor con-tractor who has undertaken to keep a window box gay with fresh blossoms; each plant must be removed almost before be-fore Its flowers fade. But our present conoern is with the fact rather than with explanation of the faot Taking the needs of reproduction as a master key, we find it unlocking the secrets of inequalities of life. The May flies live only a few hours, but their eggs are produoed abundantly and have only to be dropped into pools from which their parents, leaving their chrysalis, chrys-alis, sprang into the sunny air. The short lived moths and butterflies similarly simi-larly are untroubled by family cares. When the eggs have to be deposited on common and abundant food plants the females need and possess few hours in which to accomplish their easy task. The males, on the other hand, have to fly about seeking and sometimes fighting fight-ing for possession of the females, and to them a longer life is allotted. Butterflies But-terflies and moths that live for more than a few days are those whose caterpillars cater-pillars require a rarer food plant, a more carefully chosen nursery and feeding feed-ing ground. The females have to fly about seeking convenient spots for their offspring, and the eggs, instead of ripening ripen-ing and being deposited simultaneously, simultaneous-ly, are laid from day to day until the full tale be accomplished. In many tribes of bees the males play their part but once, and that during the nuptial flight of the queen. Immediately afterward after-ward they die or shortly after are killed by the workers. The queens, secluded in the middle of the hive, produce crops of workers year after year, and so their lives are prolonged. Among the birds and beasts parental cares have brought length of days with tbem. The small singing birds are rapid breeders, sometimes produoing five or sex nestlings twice a year, but their enemies are equally numerous, and despite de-spite the constant attention of the male and female play such havoo with the youug that hardly in 20 years will a pair rear up young enough to maintain the species. Birds like pheasants and fowls are still more prolific, but old and young like are preyed upon by a multitude mul-titude of enemies. The birds of prey are slow breeders. Their active flight makes it impossible that the females should carry with them a burden of developing eggs, and in their long lives they leavj bohind them no more progeny than quicker breeding, shorter lived orea-turea orea-turea Saturday R.ev lew. |