244 PRESENT-DAY RATIONALISM 



cisely the same kinds of nests, as of thrushes, blackbirds, 

 rooks, etc., respectively. Evolution will not allow that 

 any particular kind of bird ^rst built one of the shape 

 and structure now peculiar to the species, other than as 

 a result of experiment. I mean, the bird could not have 

 had any previous instruction as to how it should be built. 



But having once succeeded to its satisfaction, the 

 same nest becomes, so to say, an hereditary feature ; and 

 the power to make it an heirloom. 



It is thought the young birds receive instruction from 

 their parents. It is very possible, not to say likely, that 

 such is the case ; but experiments have shown that it is 

 not always necessary. Thus a greenfinch's &^^ hatched 

 under a canary proved to be a hen and subsequently 

 built a normal greenfinch's nest, A young bullfinch 

 taken early has been known to do the same thing. 



Whether trap-door spiders learn how to make nests, 

 I do not know, but those of very small spiders I possess 

 are just as beautifully made as if by full-grown individuals. 



Similarly, habits of instinct seen in insects seem to 

 have been originally successful experiments, which having 

 proved to be useful are repeated ad infinituvi by heredity. 

 Thus certain wasps paralyse spiders, but do not kill 

 them, for food for their grubs. The exact spot where 

 the nerve ganglion is may have been originally found by 

 " trial and error " ; but once discovered, the stinging the 

 victim there has become hereditary. 



Birds and insects are said to change their usual habits 

 if they alter their habitats, if it be necessary to do so, 

 under the influence of the environmental conditions ; just 

 as their own bodies become modified giving rise to new 

 varieties or species. 



It is said, for example, that the hive-bee has been 

 known to abandon the hexagonal cell, and lapse into 



