LORD SALISBURY ON EVOLUTION. 579* 



divisible into 403,200 changes each occupying a minute. No one 

 of these changes is appreciable by the naked eye, or even by a 

 micrometer. Turn now to the other member of the comparison. 

 Let us suppose the total change between the primitive Protozoan, 

 or nucleated cell, and the human being proceeding from it, to be 

 divided into increments of change, equal in their number to those 

 gone through by the foetus. To compare the two sets of changes 

 we divide 100,000,000 years by 403,200. What is the result ? We 

 get nearly 250 years as the interval available for an amount of 

 change equal to that which the foetus undergoes in a minute. 

 Another way of presenting the facts yields results still more 

 striking. Many creatures of superior types take more than a year 

 to reach the reproductive age, and even among insects there are 

 some which retain their larval forms for a longer period. But, 

 bearing in mind that even among the Vertebrata the immense 

 majority of species reach the reproductive age in a year, while 

 some of them, as the inferior Rodents, reproduce in a shorter 

 term, and remembering that throughout the lower divisions of 

 the undetermined phylogenetic series preceding the vertebrates, 

 consisting of relatively small and simple creatures, the succession 

 of generations was probably more rapid, we may fitly, contem- 

 plating the whole series, take a year as the equivalent for a gen- 

 eration. If so, it follows that to achieve the transformation of 

 the Protozoan into Man, it requires only that in the space of 250 

 generations the change shall be as great as that which the human 

 foetus undergoes in a minute ; or, otherwise stating the fact, it 

 requires that each generation shall differ from the last by as 

 much as the foetus differs from itself after an interval of a fourth 

 of a second. 



Should it be urged that the successive stages of the transfor- 

 mation gone through by the infant do not represent fully the 

 stages of transformation gone through in progressing from the 

 primitive nucleated cell to the human being, but that there have 

 been periods of excursive modification on various sides of the 

 direct line, and periods in which there was no advance, or in 

 which there was even some retrogression, it would still result that 

 if, in one generation, there occurred as much change of form as 

 the foetus undergoes in a minute, the remaining 240 odd genera- 

 tions might be set aside for non-progressive changes : a sufficiently 

 wide margin. 



One more misconception embodied in Lord Salisbury's address 

 remains to be noted not a misconception peculiar to himself, but 

 one which men at large entertain. Speaking of the groups of 

 chemical elements, he says : 



"The discovery of these co-ordinate families dimly points to some idea- 



