210 Education through Nature 



and consequently will be able to withstand the en- 

 croachments of weeds, that are sure to appear on the 

 scene when the bean-patch is not well cultivated by 

 the owner. The appearance of weeds is much like 

 the arrival of an enemy. A conflict ensues between 

 the bean and the weed as to which shall have most 

 soil, most rain, and most sunshine. The weak bean, 

 which is not adapted to the conditions of life, will 

 succumb in this struggle and will produce no flower 

 and no fruit. 



This struggle is called the " struggle for existence"; 

 and the success of the strong bean, the failure of 

 the weak, is called " natural selection" or " Survival 

 of the Fittest." 



IV. Some Important Facts in the Life of Animals. 



Animals, like plants, are composed of either a single 

 cell, as in the Protozoa, or of aggregations of cells 

 or tissues, as in the Metazoa. The life of the animal, 

 like the life of the plant, resides in this ultimate unit, 

 the cell. The cell is the bridge which spans the 

 chasm between one generation and the next. In the 

 plant this bridge may be a spore, a single cell; or it 

 may be the seed, a large aggregation of cells forming 

 an embryo. In the animal, too, it may be a spore, 

 or an egg, which is often only a cell, but frequently 

 a cell with many accessory parts, and often with a 

 partly formed embryo, as in the hen's egg. 



In either case life is continuous, being associated 

 with that primitive organic substance called proto- 

 plasm. It is now maintained that all life, plant or 

 animal, springs from some preceding life, the parent, 

 the seeds or eggs being little particles detached, like 

 buds, to give rise to new organisms. 



Good examples of these reproductive bodies are 

 afforded by frog-spawn. This is very common in 



