(Greek: physiologos, one who discourses on nature)
A collection of Christian allegories dating probably from the 2nd century in which religious truths are symbolized by animals, e.g., Christ's saving of mankind by His Crucifixion is represented by the pelican who feeds its off-spring by shedding its own blood.
It derives its name from the introductory phrase of each tale "the physiologus (naturalist) says..."
Various translations and adaptations of the original Greek text have been made and the numerous Bestiaries derived much of their material from it.
It was universally popular in the Middle Ages and exerted a wide influence on medieval literature and ecclesiastical art.
New Catholic Dictionary