156 CHILDHOOD OF ANIMALS 



sometimes on the ground and sometimes on trees. Closely allied 

 species in many cases show great differences in their choice of 

 nesting-places and in the nature of the preparation they make. 

 Habits and surroundings may thus change very quickly, much more 

 quickly than we can suppose structure and function to change, 

 and colours and patterns that had fitted a former environment 

 may seem strange and unsuitable in a new environment. No doubt, 

 if they were very unsuitable, the old colours and patterns might 

 lead to the extermination of their owners, before they could be 

 changed. But equally possibly the advantages of the new habit 

 or new surroundings might be so great that they would counter- 

 balance the garb that had lost its suitability. Birds are a highly 

 successful branch of the animal kingdom, with great powers of 

 locomotion and with great capacities for adapting themselves to 

 new circumstances, and we might well expect to find amongst 

 them many cases where coloration had outlived the conditions 

 to which it was suited. 



I hesitate, therefore, to throw overboard the conception that 

 the coloration of the eggs of birds is adaptive. In many cases it 

 is extremely suitable, and there may be other cases where it was 

 recently suitable. I prefer to see in it, however, another instance 

 of the change from the plain to the coloured, from the dull to the 

 gay. It is a process not designed for the pleasure of man, although 

 in many cases it delights his eye. It is a process which, so far 

 from necessarily being of advantage to the animals in which it 

 appears, sometimes adds to their cares, but which is occasionally 

 neutral and now and again of benefit. Eggs were at first white, 

 but there is a tendency for them to be stained with the bright exuda- 

 tions of the body, with the by-products of the vital chemistry of 

 the blood. Natural selection, so to say, has hung on the outskirts 

 of the process of change, and has retarded it where its results were 

 dangerous, and has encouraged it where they were useful, and 

 where they were indifferent it has left matters to their natural 

 course. 



When the eggs have been laid, they have to be kept warm until 

 they hatch, a duty that is avoided only in a few rare cases. Birds 

 are even more hot-blooded than mammals ; it is not always easy to 

 take their temperature accurately, as the act of handling them 

 excites them and raises the temperature, but it seems to range 

 from the human normal to about 104 or 105 Fahr. The eggs 

 must be kept at temperatures approaching or surpassing these 



