1884.] 
737 
An Exegesis of Darwinism. 
and vegetable kingdoms ” (p. 50) ; and as “ it may meta- 
phorically be said that natural selection is daily and hourly 
scrutinising, throughout the world, the slightest variations” 
(p. 65) ; and as organisms “ have to struggle for existence 
from the hour of their birth to that of their death ” (ii., 
219), one would, variation granted, anticipate incessant se- 
lection. 
It appears, however, that “ the war of Nature is not in- 
cessant ” (p. 61), and also (from the text of the diagram) 
that variations occur “ often after long intervals of time ” 
(p. 90), notwithstanding the fact that there is much super- 
ficial probability in the theory that variation is necessarily 
contingent on reproduction (ii., 239, 240). Moreover, al- 
though “ mere lapse of time by itself does nothing” (p. 82, 
&c.), yet every form will, during each successive age, have 
to be slightly modified ” (p. 308). 
An Exegesis of the diagram may illuminate matters. Its 
construction betrays care. The relative length of b, c, d 
with g, h, and b, c, d and g, h inter se ; the extension of F 
to F 1 4 rather than of E to E 14 , correspond with the text. If 
of a dozen species, a couple alone were ever beset with 
favourable variability never witnessed by their fellow-species 
during an aggregate existence of 36,000 generations ; and if 
by an acceleration of variability the fourteen new forms 
were ever evolved from five in less than half the number of 
generations taken by the five to diverge from two, then the 
diagram corresponds with Nature. 
14. “ We clearly see that the nature of the conditions is 
of subordinate importance, in comparison with the nature 
of the organism, in determining each particular form of 
variation ; perhaps of not more importance than the nature 
of the spark, by which a mass of combustible matter is 
ignited, has in determining the nature of the flames ” (p. 8, 
ii., 281, &c.). As already stated, this section is really one 
with 12. 
15. “ Every variation is either directly or indirectly caused 
by some change in the surrounding conditions ” (ii., 415). 
“ These several considerations alone render it probable that 
variability of every kind is directly or indirectly caused by 
changed conditions of life. Or, to put the case under 
another point of view, if it were possible to expose all the 
individuals of a species during many generations to abso- 
lutely uniform conditions of life, there would be no varia- 
bility ” (ii., 242). Such changes, however, operate as a rule 
not upon the varying individual itself, but upon the parents 
or their reproductive organs (ii., 35, p. 260 ; cf. ii., 2 57), 
