It was Jaeger who once, said - but I forget where - that enough had been done in the way of philosophising by Darwinists, and that the task that now lay before us was to apply the test of exact investigation to the hypotheses we had laid down.<br><br>I have long been of the same opinion; but it is in fact a thing much easier said than done. It is infinitely easy to form a fanciful idea as to how this or that fact may be hypothetically explained, and very little trouble is needed to imagine some process by which hypothetical fundamental causes - equally fanciful - may have led to the result which has been actually observed. But when we try to prove by experiment that this imaginary process of development is indeed the true and inevitable one, much time and laborious research are indispensable, or we find ourselves wrecked on insurmountable difficulties.<br><br>Nevertheless the step must be taken.