Teratology (Gr. τέρας, a wonder or monster, and λόγος, discourse), that branch of physiological science which treats of the malformations and monstrosities of plants and animals. On account of its greater interest, more attention has been given to the latter, particularly within the present century, by French and German physiologists. There was no attempt to systematize the study of monstrosities till the time of Isidore Geoffroy Saint-Hilaire, who gave the science the above name. His classification is given in the article Monster. He divides the history of monstrosities into three periods, viz.: the fabulous, the positive, and the scientific. The fabulous period is all that prior to the 18th century; the positive embraces the first half of the 18th century; while the scientific dates from the middle of that century. In the fabulous period the prevalent belief attributed the formation of human monsters to divine anger as punishments to parents, or to demoniacal influence, and as the progeny of the devil they were destroyed. As late as the beginning of the 17th century it was said by learned men that children with six fingers were made in the image of the devil, and a remnant of such superstition still exists.

The first important work was published by Leicetus in 1616, in which he gives a great collection of the most fabulous monsters, He quotes largely from a work on monsters by Lycosthenes (1557), and his pages abound in wonders. A work published by Haller in 1768 is the first which may be regarded as scientific. Buffon gives a classification of monsters in his "Natural History." Meckel, the celebrated physiologist, published a complete treatise on monsters in his Handbuch der pa-thologischen Anatomie (1812-'18), and Tiede-mann makes important observations on the genesis of monsters in his Anatomie der kopf-losen Missgeburten (1813). Works of the greatest importance were those of the two Geoffroy Saint-Ililaires (1822, 1829, and 1832-'6). A work on monsters in Dutch and Latin, by W. Vrolik, is one of the most complete manuals on teratology (Amsterdam, 1840-'42; new ed., fob, with 100 plates, 1849), and contains the most complete atlas that has ever been published. See also articles in the transactions of the New York state medical society for 1865, '66 '67, and '68, on "Diploteratology," by Dr. J. G. Fisher of Sing Sing, N. Y., giving a brief history of the subject of teratology, adding to the classification, and giving also the history of many cases of double monsters; J. North, "Lectures on Monstrosities" (London "Lancet," 1840); Allen Thompson, "Remarks upon the Early Condition and Probable Origin of Double Monsters," in "London and Edinburgh Monthly Journal of the Medical Sciences " (1844); J. Vogel, Pathologische Anatomie des Menschlichen Korpers (Leipsic, 1845); C. Rokitansky, Lehrbuch der pathologischen Anatomie (Vienna, 1851 - '61); William F. Montgomery, "Account of a very remarkable Case of Double Monster," etc, in "Dublin Quarterly Journal of the Medical Sciences" (1853); A. Forster, Die Missbildungcn des Mensclien (2 vols. 4to, with 2G plates, Jena, 1861); and M. Lerboullet, Recherches sur les monstruosites du brocket observees dans l'oeuf, et sur leur mode de production, in the Annales des sciences na-turelles (Paris, 18G3).