204 PRESENT-DAY RATIONALISM 



a new structure is to be acquired to suit the habit and conveni- 

 ence of the organism. 



Besides hereditary structures and habits, hereditary skill 

 must be observed. Young birds can build just as good nests, 

 as a rule, as the old ones. "Trap-door" spiders can make 

 exquisite " retreats," when they are quite young, in no way 

 inferior to those of adults ; though it is said that they are not 

 always equally so ; and are consequently sometimes more easily 

 discoverable by their enemies. Still the difference between a 

 "good" nest or retreat made as a first attempt, by an animal, 

 and the period covered by a son in learning the trade of his 

 father is very different. 



It is impossible, too, for silkworms raised in paper trays 

 from the egg to have learnt how to make their exquisite silk 

 cocoons, or spiders their geometrical webs. 



Skill is thus equally hereditary with the art itself; though 

 there is no reason for supposing these instincts to have been 

 directly impressed upon them by the Creator, but that they 

 have been acquired and perfected through generations, and the 

 skill has then become a fixed trait of their constitution and a 

 hereditary feature.^ I shall have more to say upon Instincts in 

 Part II. 



^ As I have discussed and criticised Dr. Weismann's theory of heredity 

 elsewhere, I need only refer the reader to my paper in Natural Science, 

 vol. i., p. 171. 



