334 ANIMAL LIFE 



24. VANISHING SPECIES 



The fossil remains of animal life embedded in the rocks 

 testify that more than fifty thousand species have vanished 

 within probably thirty million years. The stone records 

 indicate that during the ancient past no one species sur- 

 vived longer than two or three million years, while some 

 may have existed only a few thousand years. In the 

 earth's youth, the comparatively rapid changes in climate, 

 soil, and food, together with the appearance of new ene- 

 mies, made it necessary that any species to win in the 

 struggle for existence should change its habits and struc- 

 ture to harmonize with its environment. The penalty for 

 failure to do this was extinction. There is a continual 

 warfare in nature not only between certain different species, 

 but also among the individuals of the same species. Of 

 the one hundred or more spiders hatched from the eggs in a 

 cocoon only a few attain full size, the weaker being eaten 

 by the stronger. Of the million eggs deposited by a shad, 

 probably less than a score give rise to adults, as many will 

 die from lack of food and others must go to satisfy the 

 carnivorous appetite of larger fish. Of a dozen quail 

 reared in a single nest, only a few of the more hardy and 

 wideawake will be able to endure the rigorous winter and 

 escape the ever-pursuing enemies. The fulmar petrel is 

 one of the most abundant of birds in certain regions of the 

 seas, but the female lays only one egg yearly. It has 

 scarcely any enemies. Rabbits, though producing three 

 litters of from four to six each in a season, are on the de- 

 crease in the Eastern States, owing to the presence of 



