Page:The Scientific Monthly vol. 3.djvu/322

 3i6 THE SCIENTIFIC MONTHLY

The Obigik of Anihal Life

A prime biochemical characteristic in the origin of animal life is the derivation of energy neither directly from the water, from the earth, nor from the earth's or sun's heat, as in the most primitive bac- terial stages ; nor from sunshine, as in the chlorophyllic stage of plant life; but from its stored form in the bacterial and plant world.

We have no idea when the first unicellular animals known as protozoa appeared. Since the protozoa feed freely upon bacteria it is possible they may have evolved during the bacterial epoch ; it is known that protozoa are at present one of the limiting factors of bacterial activity in the soil and it is even claimed* that they have a material effect on the fertility of the soil through the consumption of nitrify- ing bacteria.

On the other hand, it may be that the protozoa appeared during the algal epoch or subsequent to the chlorophyllic plant organisms w^hich now form the primary food supply of the freely floating and swimming protozoan types. A great number of primitive flageUates are sapro- phytic, using only dissolved proteids as food.''

"Apart from the parasitic mode of deriving their energy, even the lowest forms of animal life are distinguished both in the embryonic and adult stages by their locomotive powers. Heliotropic or sun reactions, or movements towards sunlight, are manifested at an early stage of animal evolution. In this function there appear to be no boundaries between animals and the embryos of plants.^ As cited by Loeb and Wasteneys, Paul Bert in 1869 discovered that Daphnia swims towards the light in all parts of the visible spectrum, but most rapidly in the yellow or in the green. More definitely, Loeb observes that there are two particular regions of the spectrum, the rays of which are especially effective in causing organisms to turn, or to congregate, towards them: these regions lie (1) in the blue, in the neighborhood of a wave-length of 477 /4f^ and (2) in the yellowish-green, in ihe region of A = 534fifi; and these two wave-lengths affect different organisms, with no very evident relation to the nature of these latter. Thus the blue rays (of 477 /ifi) attract the protozoan infusorian Euglena, the hydroid coelenterate Eudendrium, and the seedlings of oats; while the yellowish-green rays (of 534 /ifi) in turn affect the protozoan Chlamydomonas, the little water-fiea Daphnia (crustacean), and the larvae of barnacles (crustacea).

Aside from these heliotropic movements which they share with plants, animals show higher powers of individuality, of initiation, of

oBussell, Edward John, and Hutchinson, Henry Brougham, 1909, p. 118; 1913, pp. 191, 219.

1 G. N. Calkins.

8 Loeb, Jacques, and Wasteneys, Hardolph, 1915. 1, pp. 44-47; 1915. 2, pp. ^28-330.

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