WORLD-MAKING 25 



it may be made to move with a touch. So it probably is with 

 organisms. But if so, then the causes of variation are external, 

 as in many cases we actually know them to be, and they must 

 depend on instability with change in surroundings, and this so 

 arranged as not to be too extreme in amount, and to operate 

 in some determinate direction. Observe how remarkable the 

 unity of the adjustments involved in such a supposition ! — 

 how superior they must be to our rude and always more or less 

 unsuccessful attempts to produce and carry forward varieties 

 and races in definite directions ! This cannot be chance. If 

 it exists, it must depend on plans deeply laid in the nature of 

 things, else it would be most monstrous magic and causeless 

 miracle. Still more certain is this conclusion when we con- 

 sider the vast and orderly succession made known to us by 

 geology, and which must have been regulated by fixed laws, 

 only a few of which are as yet known to us. 



Beyond these general considerations we have others of a 

 more special character, based on palseontological facts, which 

 show how imperfect are our attempts as yet to reach the true 

 causes of the introduction of genera and species. 



One is the remarkable fixity of the leading types of living 

 beings in geological time. If, instead of framing, like Haeckel, 

 fanciful phylogenies, we take the trouble, with Barrande and 

 Gaudry, to trace the forms of life through the period of their 

 existence, each along its own line, we shall be greatly struck 

 with this, and especially with the continuous existence of many 

 low types of life through vicissitudes of physical conditions of 

 the most stupendous character, and over a lapse of time 

 scarcely conceivable. What is still more remarkable is that 

 this holds in groups which, within certain limits, are perhaps 

 the most variable of all. In the present world no creatures 

 are individually more variable than the protozoa; as, for 

 example, the foraminifera and the sponges. Yet these groups 

 are fundamentally the same, from the beginning of the Palaeo- 



