At one period certain phenomena of nature, such as an eclipse or comet, were thought to exercise their influence on monstrous births.

Rueff mentions that in Sicily there happened a great eclipse of the sun, and that women immediately began to bring forth deformed and double-headed children.
Before ending these preliminary remarks, there might be mentioned the marine monsters, such as mermaids, sea-serpents, and the like, which from time to time have been reported; even at the present day there are people who devoutly believe that they have seen horrible and impossible demons in the sea.

Pare describes and pictures a monster, at Rome, on November 3, 1520, with the upper portion of a child apparently about five or six years old, and the lower part and ears of a fish-like animal.

He also pictures a sea-devil in the same chapter, together with other gruesome examples of the power of imagination.
Early Teratology .-- Besides such cases as the foregoing, we find the medieval writers report likely instances of terata, as, for instance, Rhodiginus, who speaks of a monster in Italy with two heads and two bodies; Lycosthenes saw a double monster, both components of which slept at the same time; he also says this creature took its food and drink simultaneously in its two mouths.

Even Saint Augustine says that he knew of a child born in the Orient who, from the belly up, was in all parts double.
The first evidences of a step toward classification and definite reasoning in regard to the causation of monstrosities were evinced by Ambroise Pare in the sixteenth century, and though his ideas are crude and some of his phenomena impossible, yet many of his facts and arguments are worthy of consideration.