408 THE WONDER OF LIFE 



colour ; or (2) there is an overlaying of the old colouring 

 and pattern by something distinctively new, ' ruptive ', as 

 he calls it. The new types of colouration are increasingly 

 utilitarian and are proportionately defined by Natural 

 Selection. We say ' new ', but what occurs is probably 

 an analysis of the ' old ' ; certain factors come to the front 

 and others recede. Chalmers Mitchell uses the very 

 instructive analogy perhaps, as he hints, much more 

 of the dull coal-tar residues from which have been analysed- 

 out the ail-too vivid aniline dyes. In various passages, 

 somewhat neutralized (we think) by others, Darwin suggests 

 the view which many of his disciples hold (sometimes as if it 

 were their own), that the colours and patterns of animals 

 are outcrops of the dynamic constitution of the creature, 

 or by-products, it may be, of its activity ; but that what 

 happens and has happened in Nature's sifting may be 

 described as an elimination of the fatally exuberant or 

 conspicuous. 



The Purpose of Youth. As we ascend the scale of 

 animal evolution, we find that one of the tendencies, most 

 notable in Mammals, is to lengthen out the duration of 

 youth. All sorts of devices and precautions conspire to 

 secure that the young animals remain longer young fed, 

 protected, freed from care and responsibilities, dowered 

 with energy, and given opportunity to play. We owe 

 to Groos, in particular, the idea that the play-period is the 

 educative period in the truest sense, and of fundamental 

 importance to the subsequent life. 



We have discussed the matter recently in our Biology 

 of the Seasons. 



' There are many play-instincts among animals ; they 

 have been wrought out in the course of ages, partly 



