288 
HALF HOUKS WITH INSECTS. [Packard. 
same thought were taken up in successive geological periods, 
and worked out in different ways, but with the same funda¬ 
mental plan. The plan is the result of an unbroken line of 
forms transmitted by genetic descent; the variations in the 
typical forms have been induced by changes in the soil and 
air. These lines of development, from so-called archetypal 
forms suddenly stop, and we have to follow them back before 
we can again take up the thread of development of other 
lines. There is not a continuous chain of being, but lines 
of development sometimes parallel, but more often diverging 
and connected by cross ties and branches linking the animal 
creation into a whole, all converging to a primordial ances¬ 
tor, perhaps no more highly organized than the structureless 
Moner, a drop of living, moving, self-reproducing proto¬ 
plasm. 
Turning now to the cases of mimicry in the butterflies 
described by Messrs. Bates and Wallace and Trimen, from 
South America, the East Indies and South Africa, respec¬ 
tively, all agree that the Heliconidm are mimicked by other 
butterflies which are very unlike the members of their own 
families, and copy in form and color the Heliconidse which, 
probably owing to a bad odor, are not eaten by birds, and 
thus multiply in great abundance. The object of the mimic 
is claimed to be a utilitarian one. It flies about in the dis¬ 
guise of a Ileliconia, and were it not for this protection it 
and its offspring would become extinct. This resemblance, 
moreover, lias probably, these authors claim, been brought 
about by natural and sexual selection. In the beginning 
some butterfly, through the tendency to variation assumed 
by Mr. Darwin, had a remote resemblance to a Heliconia; 
this favored it above its fellows, and the character growing 
more strongly marked became perpetuated, until after a 
great number of generations the similarity of form became 
perfected. Mr. Darwin adopts the view, and regards the 
mimicry as brought about by natural and sexual selection. 
32 
