O. G. Dely szerk.: Vertebrata Hungarica 21. (Budapest, 1982)
Adler, Kr.: Sensory aspects of Amphibian navigation and compass orientation 7-18. o.
Pineal extraocular photoreceptors (EOPs) in amphibians have been implicated in several activities including (1) neurosecretory activity in the central nervous system; (2) body-lightening reactions in larvae; and (3) cuing of circadian rhythms. Tn orientation, EOPs are utilized in perception of celestial cues for use in time-compensated compass orientation. Although there is evidence that under natural skies polarized light can be detected extraocularly and used for orientation by bullfrog tadpoles (TAYLOR & AUBURN 1978), there is no comparable evidence for the detection of the sun cue itself by EOPs. Use of Magnetic Cues for Orientation Possible use of the earth's magnetic field in animal orientation was proposed over a century ago but only recently have unequivocal data been obtained (see several papers in SCHMIDT-KOENIG & KEETON 1978). The first evidence among Amphibia was for cave salamanders (Plethodontidae: Eurycea luctfug a), a species spending at least part of its annual cycle deep in the lightless regions of caves (PHILLIPS 1977). In these tests salamanders were trained in dark, elongate corridors by alternately drying and moistening the ends of the corridors, forcing the animals to move back and forth along a desired axis. When tested, the animals were placed in an assembly permitting them to move in any of four directions (Fig. 6). The test assembly was situated inside a series of coils which made it possible, when the current was turned on, the induce a magnetic field whose axis differed from that of the earth's by 90°. MELANOPHOftES <Pigmant> FRONTAL ORGAN <Stirnorgan> • FRONTAL NERVE <N*rvua pinaali» SKULL <ScrukMridK*> PINEAL TRACT <Tractus pinaalis> TECTUM <T«ctum> PARAPHYSIS PINEAL BOO* <Epiphysts cerabn) CEREBRUM <Grot»hirn> OPTIC NERVE <N*rvu* opMcu» Fig. 5. Gross morphology of the pineal complex in frogs (Rana ). Median sagittal section through frog's brain (left to right: telencephalon to mesencephalon). Dermal melanophores are reduced in abundance near the frontal organ, creating the so-called "brow spot" which is easily visible on top of the head in many species of frogs. The pineal systems of salamanders and caecilians differ primarily in the absence of the frontal organ and nerve. Adapted from ADLER (1976) after van de KAM ER
