144 THE HAUNTS OF LIFE 
gins to form within the egg. For every ani- 
mal in its early life tends in a greater or less 
degree to repeat in its personal history some 
of the stages that have been gone through in 
the history of its race, and much of this can 
be made out by a careful study of the stages 
that appear, often to disappear again very 
quickly, in the earlier period of the building 
up of the body of the individual. 
The same thing is true to some extent of 
habits, and, in particular, many animals have 
an impulse to go back at the breeding-season 
to bring forth their young in the place where 
they themselves first began life. Therefore, 
when we find an animal leaving the haunt in 
which the greater part of its life is passed, 
to bring forth its young in quite a different 
one, we have good grounds for believing that 
its ancestors once had their home in the haunt 
to which it returns. 
But there is a difficulty here which must be 
faced. There are some cases in which the 
youthful stages are passed in a haunt which 
was certainly not the original headquarters. A 
good illustration of this may be found in in- 
sects like May-flies and Dragon-flies, Caddis- 
flies and Alder-flies, Gnats and Harlequin- 
