very abnormal forms are
sterile, but there are instances where they reproduce their kind and
become a species.[35] Geoffroy St. Hilaire, who perhaps made the deepest
investigations ever conducted into the nature and causes of their
production, first conceived the idea of artificially producing them, and
to this end he began modifications of the physical conditions of the
evolution of the chicken during natural and artificial incubation. He
determined the fact that monsters could be produced in this way, but
scarcely carried his investigation further. This work has been taken up
by M. Dareste, and he has lately published a volume in Paris which
recounts the results of a quarter of a century's experimenting. Eggs, he
states, were submitted to incubation in a vertical instead of a
horizontal position; they were covered with varnish in certain places so
as to stop or modify evaporation and respiration. The evolution of the
chick was rendered slower by a temperature below that of the normal heat
of incubation. Finally, eggs were warmed only at one point, so that
the young animal, during development, was submitted at different
parts to variable temperatures.

[Illustration: Fig. 1.]

[Illustration: Fig. 2.]

[Illustration: Fig. 3.]

[Illustration: Fig. 4.]

[Illustration: Fig. 5.]

[Illustration: Fig. 6.]

[Illustration: Fig. 7.]

[Illustration: Fig. 8.]

These perturbations resulted in the most curious and unlooked for
deformities in the embryo, some being not alone peculiar to the bird,
but being similar to those which have been recognized in many other
animals, and even in the human species. The data obtained have been
deemed so important that M. Dareste has recently received the Lacaze
prize for physiology from the French Academy of Sciences.

It would be impossible to review even a fraction of the many forms of
monstrosities which M. Dareste has discovered. Those that we give will,
however, suffice to convey an idea of the wonderful variations produced.
Fig. 1 is a chick embryo with the encephalon entirely outside the head,
the heart, liver, and gizzard outside the umbilical opening, right wing
lifted up beside the head, and the development of the left one stopped.
In Fig. 2 the encephalon is herniated and marked with blood spots, the
eye is rudimentary and replaced by a spot of pigment, the upper beak is
shorter than the lower one, while the heart, liver, etc., are all
outside. In Figs. 3 and 4 the he