Fig. 6. The eyes of canines. The red fox (Vulpes vulpes) has vertical slit pupils and multifocal optical systems (A,B). Grey wolves and dogs (Canis lupus lupus and Canis lupus familiaris, respectively) have circular pupils (D). The status of their optical systems is unclear, because some dogs have smooth photorefractive reflexes (dachshund; C), while others have clear ring-like structures (giant schnauzer; E). All members of a group of four closely related tame wolves had a central region of irregularity in photorefractive images (F). Scale bars are 5 mm.