624 THE AMERICAN NATURALIST. [VOL XXXII. 
to inquire into the present state of evolution and its usefulness 
to zodlogists as a working theory, and then to dwell more at 
length on the subject of the effect of geological changes on 
animal life. 
The two leading problems which confront us as zodlogists 
are: What is life? and How did living beings originate? 
We must leave to coming centuries the solution of the first 
question, if it can ever be solved; but we can, as regards 
the second, congratulate ourselves that, thanks to Lamarck, 
Darwin, and others, in our day and generation a reasonable 
and generally accepted solution has been reached. 
Time will not allow us to attempt to review the discoveries 
and opinions which have already been discussed by the founders 
and leaders of the different schools of evolutionary thought, and 
which have become the common property of biologists, and are 
rapidly permeating the world’s literature. 
It may be observed at the outset that, if there is any single 
feature which differentiates the second from the first half of 
this century, it is the general acceptance of the truth of epi- 
genetic evolution as opposed to the preformation or incasement 
theory, which lingered on and survived until a late date in the 
first half of the present century.! The establishment of the 
1 The theory of incasement (eméoftement), propounded by Swammerdam in 
1733, was that the form of the larva, pupa, and imago of the insects preéxisted 
in the egg, and even in the ovary ; and that pe insects in these stages were dis- 
tinct animals contained one inside the other, like a nest of boxes, or a series of 
envelopes one within the other; or, in his words: “ Animal in animali, seu pig 
lio intra erucam reconditus.” Réaumur (1734) also believed that the caterpillar 
contained the form of the chrysalis and butterfly, saying: “ Les parties des papil- 
lon cachées sous le fourreau de chenille sont d’autant plus faciles 4 trouver que 
la transformation est plus proche. Elles y sont néanmoins de tout temps.” He 
also believed in the simultaneous existence of two distinct beings in the insect. 
“ Il serait très curieux de connaître toutes les communications intimes qui sont 
entre la chenille et le papillon. . . . La chenille hache, broye, digére les aliments 
qu’elle distribué au papillon; comme les méres préparent ceux qui sont portés 
aux foetus. Notre chenille en un mot est destinée à nourrir et à défendre le papil- 
lon qu’elle renferme.” (Tome i, 8e Mémoire, p. 
It was not until 1815 that Herold exploded this error, though Kirby and Spence 
in 1828, in their Zztroduction to Entomology, combated Herold’s views and ma ain- 
tained that Swammerdam was right. As late as 1834, a century after Swammer- 
dam, Lacordaire in his Zzźroďuction à 1 Entomologie, declared that “a caterpillar 
is not a simple animal, but compound,” and he actually goes so far as to say that 
