Page:Popular Science Monthly Volume 45.djvu/461

 appeal must not itself be submitted to investigation and statement—to theory—strikes me as decidedly naïve.

Here as elsewhere our greatest need is to make our theories submit to the test of practice, to experimental verification, and, at the same time, make our practice scientific—make it the embodiment of the most reasonable ideas we can reach. The ultimate test of the efficacy of any movement or method is the equal and continuous hold which it keeps upon both sides of this truth.



HERE is, perhaps, no way in which one can obtain a more vivid idea of the intensity of the struggle for existence among organic beings than by the study of the inhabitants of a freshwater pond of long standing. Every inch of space in such a situation is teeming with life, both animal and vegetable, and the chief delight of most of the animals present is to wage a ceaseless warfare upon their weaker fellows. It is an aquatic rendition of Edwin Arnold's aërial drama:

 ... Then marked he, too, How lizard fed on ant, and snake on him, And kite on both; and how the fish-hawk robbed The fish-tiger of that which it had seized; The shrike chasing the bulbul, which did hunt The jeweled butterflies; till everywhere Each slew a slayer and in turn was slain, Life living upon death. So the fair show Veiled one vast, savage, grim conspiracy Of mutual murder, from the worm to man. Who himself kills his fellow."

The largest insects occurring in our fresh-water ponds are the giant water bugs—a family of peculiar creatures, armed with immense front legs fitted for grasping and clasping their victims, and a piercing, dagger-like beak which serves both to strike the prey and as a sucking tube to extract its juices, and which also appears to be provided with poison glands which make more sure the effect of every thrust.

Three species of these bugs occur in the Northern United States. Two of them are very large and closely resemble each other; the third is much smaller, less than half the size of the others. The commoner of the larger ones in the more northern States is represented natural size in Fig. 1. It is called by entomologists Belostoma americana, or the American belostoma. It is 