654 Studies in the Theory of Descent. 



tendency to variation conformable to law." * On 

 the contrary, it is to me easily conceivable that 

 we only learn to analyse the processes of nature 

 in detail very slowly, because of their necessary 

 complexity. It thus appears to me quite useless 

 when in this sense Wigand makes use of the 

 objection, that "the gooseberry has not under- 

 gone any enlargement since 1852, although it is 

 inconceivable why it should not attain the size of 

 a pumpkin if variability was not internally limited." 

 It may well be that this is fqr the present " incon- 

 ceivable;" nevertheless, this does not justify us 

 in setting up a hypothetical " force of variation " 

 which will not admit of the gooseberry surpassing 

 the pumpkin in size. We are bound to maintain 

 that it is the action and reaction of known forces 

 which sets a limit to the enlargement of this fruit. 

 In more simple instances the causes of such 

 limitations to growth can be well perceived. 

 Several decades have passed since Leuckart 

 proved in how exact a relation the proportion of 

 volume and surface stood to the degree of organi- 



3 [The above views on the nature of variability, which were 

 also broadly expressed in the first essay " On the Seasonal 

 Dimorphism of Butterflies" (pp. 114, 115), are fully confirmed 

 by Herbert Spencer (loc. cit. chaps, ix. and x.), and more 

 recently by A. R. Wallace in an article on " The Origin of 

 Species and Genera" (Nineteenth Century, vol. vii., 1880, 

 p. 93). See also some remarks by Oscar Schmidt in his 

 " Doctrine of Descent and Darwinism," Internal. Scien. Ser. 

 3rd. ed. 1876, p. 173. R. M.] 



