THE MULTIPLICATION OF ANIMALS AND SEX 61 



36. The number of young. There is great variation in the 

 number of young produced by different species of animals. 

 Among the animals we know familiarly, as the mammals, 

 which give birth to young alive, and the birds, which lay 

 eggs, it is the general rule that but few young are pro- 

 duced at a time, and the young are born or eggs are laid 

 only once or perhaps a few times in a year. The robin lays 

 five or six eggs once or twice a year ; a cow may produce 

 a calf each year. Rabbits and pigeons are more prolific, 

 each having several broods a year. But when we observe 

 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 lob- 

 ster 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 white ant, which after it is full grown does nothing 

 but lie in a cell and lay eggs, produces eighty thousand 

 eggs a day steadily for several months. A large codfish 

 was found on dissection to contain about eight million 



If we search for some reason for this great difference in 

 fertility among different animals, we may find a promis- 

 ing 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 which do not care for their young, are very 

 prolific. The codfish produces its millions of eggs ; thou- 

 sands are eaten by sculpins and other predatory fishes be- 

 fore 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 young. But the eggs of the 

 robin are hatched and protected, and the helpless fledglings 

 are fed and cared for until able to cope with their natural 



