THE HISTORY OF INSTITUTIONS. 137 



custom would require some reference to the 

 Norman Conquest. Again, if we were to point 

 to the shape of the academic dress worn in 

 Oxford and Cambridge, Dr. Reich would 

 answer that this is kept up for the sake of 

 proctorial discipline. Granted that a uniform 

 is kept up for the purpose ; but why this par- 

 ticular uniform ? A glance at an academic 

 fashion-plate of the seventeenth century will 

 supply an answer, so far as the square cap is 

 concerned. There we see this cap in a shape 

 exactly intermediate between the clerical 

 berretta and its present form. 



In scientific explanation it is not enough to 

 show why some sort of thing exists or is done : 

 we must explain, if we can, why it is just this 

 and no other. The biologist does not merely 

 say that colours of animals are useful to them, 

 in the way of protection, etc. ; if he says this, he 

 is bound to show why this particular arrange- 

 ment of stripes or spots is useful to this par- 

 ticular species in its particular environment ; 

 and if he calls anything a " survival," he must 

 not be satisfied till he can show from what 

 previous condition it is a survival. And so, it 

 is not from a desire to take refuge in a vague 



