(in one volume), page 423.

Allen showed that many species of birds are more strongly coloured in the south of the United States, and that sometimes one sex is more affected than the other.

It is this last point that bears on Weismann's remarks (loc.
cit., pages 44, 45) on Pieris napi.

The males of the alpine-boreal form bryoniae hardly differ from those of the German form (var.

vernalis), while the females are strikingly different.