RELATIONS AND SURROUNDINGS. 13! 



and to differ in this respect from others? Broadly, because 

 the external conditions forced it upon them. 



In general one pair of animals, no matter how many 

 eggs are laid, will succeed, on the average, in bringing 

 only one pair of their offspring to maturity during their own 

 lifetime. The pressure of life is so great on the earth that, 

 in the main, if one species increases in numbers it does so 

 at the expense of others. This condition has been pictured 

 as a struggle for existence among the animals of the earth. 

 The great problem for parents is to bring two of their 

 kind to maturity. This will keep the species up. This 

 problem may be solved by producing many offspring 

 enough to sacrifice thousands with the chance that two 

 may survive. Many animals adopt this plan (as the 

 salmon and most insects) . The more enemies the species 

 has and the more unfavorable the general conditions, the 

 more numerous must be the progeny. Thus the length of 

 the reproductive life of the parents and the number of 

 offspring are adaptations to the severity of the struggle 

 for existence. 



It is clear from these facts that any device which 

 parents may adopt likely to bring the young more safely 

 to maturity will make for a saving in the necessary birth 

 rate. A little care of the young at critical stages saves 

 the need of so many eggs. It will also save the parent 

 a great physical drain and thus be an advantage to the 

 species. 



Parental care may take many forms. In its simplest 

 form it consists of storing an extra amount of food in each 

 egg, thus bringing the young to a better state of develop- 

 ment when it begins to depend on its own efforts. Ceph- 

 alopods, fishes, and birds have a large amount of food 

 in the egg. Insects and many other types, instead of this, 



