PARENT AND OFFSPRING 119 



bring a female python away from her eggs by offer- 

 ing her delicacies, but without success. 



The birds furnish us with the first example of a 

 definite step forward in family relationship. Not only 

 do they display signs of conjugal affection, as has been 

 shown at length in the chapter on courtship, but they 

 also give evidence of a united family life that lasts 

 at least until the young brood are capable of looking 

 after themselves completely. Birds' eggs need a 

 certain time for embryonic development, and require 

 heat in order to be hatched out. The mother-bird 

 supplies this by brooding over the eggs. As the young 

 birds are generally born in a fairly immature condition, 

 they need a good deal of attention after birth, until 

 they are fit to take care of themselves. As soon as a 

 pair of birds have mated, they set about procuring or 

 constructing a suitable nest for their future offspring. 

 Evolution is found here as everywhere. Progress not 

 only takes place along the whole line of the animal 

 series, from the lowest to the highest, but also in a 

 smaller way in each single class, the steps made 

 in different directions in the various classes often 

 overlapping. It is not at all surprising, there- 

 fore, to discover that the grade ol parental care 

 rises with the mental development in birds. But 

 while some species are careless in the placing of 

 eggs and in the after-care of their young, others, 

 on the contrary, exhibit the most intelligent fore- 

 thought. The former recall the habits of some of the 

 inferior classes of animals. Running birds, such as the 

 ostrich, rhea, and cassowary, do not build a nest, but 

 simply dig a hole in the earth or sand and place the 

 eggs within it. The care of these very often devolves 



