It has achieved semi-infinite variety. There are approximately a quarter million species of plants now known in the world. Most abundant and varied life is that of the insects who may be on their way to displace man and his fellow mammals as lords of the earth. A rough estimate of the number of species identified up to now is 800,000. Several thousand hitherto unknown are described each year. Of mammals, including man, there may be as many as 14,000 distinct species and geographic races extant. About 8,500 species of birds are catalogued. Sub-species and geographic races increase this number to about 30,000. Known fishes number 40,000 species and sub-species. Still, naturalists say, there are great mansions of life almost unknown to man. The collections of the Smithsonian Institution in Washington grow at the rate of about a million specimens a year, always including forms hitherto uncatalogued. Much of the material in the following pages is based on Smithsonian information, although other sources and personal observations have been liberally drawn upon. The Smithsonian specimens, as well as those in other museums and collections throughout the world, are types. Once they were individuals with passions, fears, hungers, perhaps some dim wonderings and questionings. The type is the eternal reality. The individual is the brief-lived example of this reality, the flame of a candle fluttering in a windy moment. I have brought together in these pages notes about the most extraordinary manifestations of nature that have come to my attention in the course of thirty years as a science reporter. Each example is, of course, based upon a distinctly individual expression of nature, but all are very much interrelated in this truly amazing world of ours. THOMAS R. HENRY _Washington, D. C._ _The Invisible Underground Jungle_ There may be as many as twenty-five million invisible plants and animals in a gram of soil about the size of a grain of sand. It would take a thousand such grains to make a marble. The population of this microscopic jungle is composed chiefly of single-celled organisms—bacteria, molds, yeasts and protozoa. Total numbers vary enormously—from time to time and place to place—chiefly because of variations in the food supply. Although thousands of species have been identified, the greater part of soil life still remains unknown. This jungle is a place of the hunter and the hunted—of an incessant and merciless struggle for survival. Invisible plants eat invisible animals and invisible animals eat invisible plants. Plants devour other plants and animals devour other animals.