28 



BLIND VERTEBRATES AND THEIR EYES. 



THE CAVE SALAMANDERS. 



The salamanders, of which there are many species in the United States, 

 habitually live under rocks, logs, and the bark of decaying trees. These all shun 

 the light except during the breeding season. Others habitually live in the water 

 and are principally nocturnal in their habits, hiding under the banks, logs, or rocks 

 in the water during daylight. The eyes of the cave salamanders of North America, 

 of which there are four species, range in their structure from the perfectly normal 

 to the most degenerate known among the Batrachia. 



Spelerpes maciilicauda (Cope) (plate i, fig. c) is common in the caves of the 

 Mississippi Valley. As far as I have been able to determine, its eyes have not 

 undergone any degeneration. It is abundant and so nearly allied to Spelcrpes 

 longicauda Green, an epigean species of very wide distribution, that formerly the 

 two were considered identical (plate 2, fig. a). 



Spelerpes stejnegeri Eigenmann (plate 1, fig. b) is found in the twilight regions 

 of the caves of southwestern Missouri. Its eyes are also normal. Other species 

 of Spelerpes ' are sometimes found in caves. 



Typhlotriton spelceus Stejneger (plate 1, fig. d) is restricted to the western 

 caves of the Mississippi Valley. It has so far been found in Marble Cave and 



Fig. 3. 



(a) Head of Spelerpes maculioiuda, 54 mm. long. (6) Head of TypMotrilon spelaus, 54 mm. long, 

 (c) Head of TyplUomolgc rathbuni, 47.5 mm. long. 



Rockhouse Cave, and smaller caves in the same neighborhood in southwestern 

 Missouri. It is found under rocks in and out of the water. This is the most 

 interesting form, inasmuch as it is a much more typical cave animal than Spclerpes, 

 but has not yet reached the degenerate condition of Typhlomolge. Its eyes are 

 apparently normal in the larva, but in the adult have undergone marked degen- 

 eration. The eyelids are disappearing and the rods and cones are no longer 

 present in the adult. The eyes of this species will be dealt with below. 



Typhlomolge rathbuni Stejneger (plate 2, fig. b) is found in the underground 

 streams near San Marcos, Texas. It has been taken from the artesian well at 

 San Marcos and a surface well. It has also been noticed in one of the caves 

 near that place, Ezel's, in which the underground water can be reached. It is 

 said to have come out of some artesian wells south of San Antonio. It is a peren- 

 nibranch and spends all of its time in the water. Its remarkably long and slender 

 legs are not able to support its body when out of the water. Figure 3 shows 



1 Bilineatus is frequently found about the caves of Bloomington, Indiana. 



