226 



EVOLUTION AND ANIMAL LIFE 



prolific, each having several broods a year. But when we ob- 

 serve the multiplication of some of the animals whose habits 

 are not so familiar to us, we find that the production of so few 

 young is the exceptional and not the usual habit. A lobster 

 lays ten thousand eggs at a time; a queen bee lays about five 



million eggs in her life of four or five years. 

 A female termite of a certain species, after it is 

 full grown, does nothing but lie in a cell and 

 lay eggs, producing eighty thousand eggs a day 

 steadily for several months. A large codfish 

 was found on dissection to contain about eight 

 million eggs. 



If we search for some reason for this great 

 difference in fertility among different animals, 

 we may find a promising clew by attending 

 to the duration of life of animals, and to the 

 amount of care for the young exercised by 

 the parents. We find it to be the general rule 

 that animals which live many years, and which 

 take care of their young, produce but few 

 young; while animals which live but a short 

 time, and w^hich do not care for their young, 

 are very prolific. The codfish produces its mil- 

 lions of eggs; thousands are eaten by sculpins 

 and other predatory fishes before they are 

 hatched, and other thousands of the defense- 

 less young fish are eaten long before attaining 

 maturity. Of the great number produced by 

 the parent, a few only reach maturity and 

 produce new j^oung. But the eggs of the 

 robin are hatched and protected, and the help- 

 less fledglings are fed and cared for until able 

 to cope with their natural enemies. In the 

 next 3^ear another brood is carefully reared, and so on for the 

 few years of the robin's life. 



Under normal conditions in any given locality the number 

 of individuals of a certain species of animal remains about the 

 same. The fish which produces tens of thousands of eggs 

 and the bird which produces half a dozen eggs a year main- 

 tain equally well their numbers. In one case a few survive 

 of many born; in the other many (relatively) sm-vive of the few 



Fig. 133.— Eggs 

 of lace-winged 

 fly, Chrysopa. 

 The eggs are 

 fastened sepa- 

 rately, for pro- 

 tection from 

 predaceous in- 

 sects, on the 

 tips of erect 

 6<lender pedi- 

 cles. 



