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BLIND VERTEBRATES AND THEIR EYES. 



RHINEURA FLORIDANA.' 



HABITS OF RHINEURA. 



Rh'meura floridana Baird is a legless, burrowing, blind Amphisbtenian lizard. 

 It is abundant in some parts of Blorida. The largest individual secured by the 

 author measured 340 mm. The tail is very short, flattened dorso-ventrally, and 

 the upper surface of its distal half is strongly rugose. Each of the transverse rings 

 is here, with numerous tubercles. The mouth is small ; the tip of the lower jaw 

 is some distance behind the tip of the upper jaw. In shape, color, and arrange- 

 ment of its dermal plates it strikingly resembles an earthworm. This resemblance 

 is heightened by its vermiform progression through the rhythmic movements of 

 its annular plates. Its forward and backward locomotion in its burrows is entirely 

 due to this vermiform movement. It burrows rapidly, and for this its small, 

 hard, conical head is well adapted. The point of the snout is turned down and 

 the head then thrust upward in a rooting fashion. An individual will readily dis- 

 appear in from half a minute to two minutes. By placing it in a glass vessel partly 

 filled with earth its burrowing can readily be seen from below. If placed on a 

 bare surface, it for a time will wriggle actively from side to side, snake fashion, but 

 without much effect as far as locomotion is concerned. The tail, under such cir- 

 cumstances, is dragged behind, as if it had no vital connection with the head. 

 Rarely there is a suggestion of a bracing with the tip of the tail against the floor. 

 In one minute an individual moved 250 mm. In an attempt at rooting, after the 

 snout had become wedged under the edge of an immovable object, the whole body 

 to the tip of the tail was repeatedly lifted off the floor. 



Rhincura is, as far as known, one of the two blind vertebrates that have been 

 found in the fossil state. Baur described a species of Rhineura (R. hatchcrii) and 

 another Amphisbsenian (Hypsorhina anligua) from the Miocene beds of South 

 Dakota. Baur says nothing concerning the dermal plates, so that nothing is 

 definitely known about the eyes of this fossil Rhineura. Since all the genera of 



the family Amjihislxenidae have rudimentary eyes, 

 the eyes were very probably degenerate before the 

 genera became separated. It seems quite certain 

 that any fossil members of an existing genus all of 

 whose living species have degenerate eyes, must have 

 had eyes that were to a greater or less extent degen- 

 erate. The time suggested by this find of Baur 

 (luring which the eyes of Rhincura have been degen- 

 of Head oi^Rhineura^ cratlug Is surprislngly long, extending as it does 

 through about 5 to 10 per cent of the formation of 

 sedimentary rocks. 

 Rhineura is a burrowing animal, and blind animals which burrow in the ground 

 are not found in naturally made caves. The latter are largely populated by species 

 that tend to hide in crevices or natural cavities under rocks. It would seem from 

 this that the cave fauna was incipient before the existence of caves, and that the 

 latter were colonized as soon as they were large enough to admit their present 

 inhabitants. 



I-'lG. 17. Side View i 



showing Surface Plates and Position of 

 Eye in Relation to them. 



See Proc. Wash. Acad. Sci., Iv. p. 533, 1902. 



