rm of Crustacea. He
cautiously remarks, however, that "the embryos and larvae observed by me
in the egg-parasites open up a new and wide field for a whole series of
such considerations; but I will suppress them, since I am firmly
convinced that a theory, which I build up to-day, can easily be
destroyed with some few facts which I learn to-morrow. Since comparative
embryology as a science does not yet exist, so do I think that all
genetic theories are too premature, and without a strong scientific
foundation."

The writer is perhaps less cautious, but he cannot refrain from making
some reflections suggested by the remarkable discoveries of Ganin. In
the first place, these facts bear strongly on the theory of evolution by
"acceleration and retardation." In the history of these early larval
stages we see a remarkable acceleration in the growth of the embryo. A
simple sac of unorganized cells, with a half-made intestine, so to
speak, is hatched, and made to perform the duty of an ordinary, quite
highly organized larva. Even the formation of the "primitive band,"
usually the first indication of the organization of the germ, is
postponed to a comparatively late period in larval life. The different
anatomical systems, _i.e._, the heart with its vessels, the nervous
system and the respiratory system (tracheae), appear at longer or shorter
intervals, while in one genus the tracheae are not developed at all. Thus
some portions of the animal are accelerated in their development more
than others, while others are retarded, and in some species certain
organs are not developed at all. Meanwhile all live in a fluid medium,
with much the same habits, and surrounded with quite similar physical
conditions.

The highest degree of acceleration is seen in the reproductive organs
of the Cecidomyian larva of Miastor, which produces a summer brood of
young, alive, and living free in the body of the child-parent; and in
the pupa of Chironomus, which has been recently shown by Von Grimm, a
fellow countryman of Ganin, to produce young in the spring, while the
adult fly lays eggs in the autumn in the usual manner. This is in fact a
true virgin reproduction, and directly comparable to the alternation of
generations observed in the jelly fishes, in Salpa, and certain
intestinal worms. We can now, in the light of the researches of Siebold,
Leuckart, Ganin and others, trace more closely than ever the connection
between simple growth and metamorphosi