PROTEUS or ()LAI, a blind, water-breathing, tailed amphi bian, inhabiting the limestone caves to the east of the Adriatic. It is a small eel-like animal, with minute limbs, the anterior pair hav ing three toes on each, the posterior two, a narrow head, with flat truncate snout, minute rudimentary eyes hidden under the skin which is pale flesh-coloured, with the short, plume-like external gills blood-red (Proteus anguinus). Proteus forms with Necturus the family Proteidae. The second genus, which is widely distrib uted in eastern North America, is more generalized in structure, having better developed limbs, with four digits, and is adapted to live in the light. Its thyroid gland is very much reduced, but, unlike the axolotl (q.v.), it cannot be transformed into a terrestrial form by feeding with thyroid. Exposure to white light causes the skin to become black, even over the eyes ; however, in red light, no blackening occurs, and the eyes grow large and functional.
In 1896 a Proteus-like Amphibian (Typhlomolge rathbuni) was unexpectedly discovered in Texas during the boring of an artesian well 188ft. deep, when it was shot out with a number of
remarkable and unknown crustaceans. This form agrees with Proteus in the absence of functional eyes, the presence of external gills, and the unpigmented skin. It differs in the short body and the long slender limbs with four to five digits. It is remarkable in having no thyroid gland at all. Whilst Proteus has lungs in addition to gills, Typhlomolge lacks the lungs, and with them the trachea and larynx. Both the Proteus and Typhlomolge are per manent larval forms.
Another blind Urodele, Typhlotriton spelaeus, is known from caves in the Mississippi valley. It has neither gills nor lungs in the adult, and is found under rocks in or out of the water. It is not allied to Proteus but to Amblystoma (see AXOLOTL). The eyes are normal in the larva, but in the adult have undergone degeneration. It is not a persistent larva.
See H. Gadow, Amphibia (Cambridge Natural History).