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.