CHAPTER IV 
THE INHERITED EFFECTS OF CHANGES INDUCED BY 
EXTERNAL FACTORS 
Ir has been pointed out that in butterflies the changes brought 
about by higher and lower temperatures give rise to forms that 
resemble southern and rorthern varieties of the same butter- 
flies. The question at once arises whether species may not 
have originated in this way. 
Fischer found that when a dark moth, produced by cold, 
was paired with another similar moth, the offsprings were also 
dark. His experiments extended, however, only to the first 
generation, and consequently the cold may have acted directly 
on the germ-cells of the parents. Highly important as this 
observation is in showing that the undeveloped germ-cells may 
be affected in the same way as the somatic tissues of the pupa, 
so that even under altered conditions the effect persists, yet the 
result as it stands does not conclusively show that permanent 
racial or specific changes have been produced in this way. 
Were such forms bred for several generations at a ‘warmer 
temperature, it is possible that they would return again to their 
original condition. The new type might persist only so long as, 
or a little longer than, the external conditions are the same as 
those that produced it. The change may represent only an 
extreme fluctuating variation that has been caused by an ex- 
ternal factor. 'The results do not appear, from this point of 
view, to belong to the kind of changes by which new species 
are made. Nevertheless the question still remains an open 
one as to whether changed external conditions may not at 
times cause more permanent effects. Some observations of 
Standfuss seem to show that such may be the case, although 
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