orn in Ferrari, Italy, in 1540, well formed, and with two sets of
genitals, one male and the other female. Pare gives a picture of twins,
born near Heidelberg in 1486, which had double bodies joined back to
back; one of the twins had the aspect of a female and the other of a
male, though both had two sets of genitals.

Scientific Teratology.--About the first half of the eighteenth century
what might be called the positive period of teratology begins.
Following the advent of this era come Mery, Duverney, Winslow, Lemery,
and Littre. In their works true and concise descriptions are given and
violent attacks are made against the ancient beliefs and prejudices.
From the beginning of the second half of the last century to the
present time may be termed the scientific epoch of teratology. We can
almost with a certainty start this era with the names of Haller,
Morgagni, Geoffroy-Saint-Hilaire, and Meckel, who adduced the
explanations asked for by Harvey and Wolff. From the appearance of the
treatise by Geoffroy-Saint-Hilaire, teratology has made enormous
strides, and is to-day well on the road to becoming a science. Hand in
hand with embryology it has been the subject of much investigation in
this century, and to enumerate the workers of the present day who have
helped to bring about scientific progress would be a task of many
pages. Even in the artificial production of monsters much has been
done, and a glance at the work of Dareste well repays the trouble.
Essays on teratogenesis, with reference to batrachians, have been
offered by Lombardini; and by Lereboullet and Knoch with reference to
fishes. Foll and Warynski have reported their success in obtaining
visceral inversion, and even this branch of the subject promises to
become scientific.

Terata are seen in the lower animals and always excite interest. Pare
gives the history of a sheep with three heads, born in 1577; the
central head was larger than the other two, as shown in the
accompanying illustration. Many of the Museums of Natural History
contain evidences of animal terata. At Hallae is a two-headed mouse;
the Conant Museum in Maine contains the skeleton of an adult sheep with
two heads; there was an account of a two-headed pigeon published in
France in 1734; Leidy found a two-headed snake in a field near
Philadelphia; Geoffroy Saint-Hilaire and Conant both found similar
creatures, and there is one in the Museum at Harvard; Wyman saw a
living double-headed snake