CAUDAL ABNORMALITY IN LIZARDS. 683 



condition in the bifid reproduced tail of a Lygosoma described in my 

 previous paper.* Such twisting may perhaps be a frequent feature in 

 connection with caudal duplicity. 



Internal Structure. — The internal structure of the reproduced tail 

 of lizards has very peculiar and constant features, which have been 

 described by Duges,f Fraisse§ and other writers. To render clear the 

 statements which will be made later on, I now quote the epitome of the 

 internal structure of the reproduced tail given in my previous paper. 



(a) The vertebral column is not renewed as such, but from the 



point of fracture an unsegmented, imperforate, and usually 

 somewhat irregular cartilaginous tube grows out in direct 

 continuation of the neural arches. This tube tapers with 

 the tail, and its lumen ends blindly near the tip. 



(b) The spinal cord is not reproduced, but the lumen of the cartil- 



age tube contains a core of connective tissue with large 

 blood vessels, which is continuous with the spinal cord of 

 the stump. In reality this core is a tube with thick walls, 

 as it contains a central lumen lined by a single layer of 

 columnar epithelial cells. This lumen is continuous with 

 that of the central canal of the spinal cord. 



(c) The innervation of the reproduced portion is effected by infil- 



tration of the spinal nerve roots from above the point of 



fracture. 

 {d) The caudal artery tmd vein of the stump grow into the 



reproduced portion and give off branches within it. 

 As in the case of the Hemidactylus, serial sections through the tails of 

 both specimens of Mabuia demonstrate the internal structure to possess 

 essentially the above features. But in each of the present specimens a 

 peculiarity exists in connection with the continuation of the epithelial 

 canal of the spinal cord. In specimen A this continuation of the canal 

 seems to be entirely absent, the connective tissue core of the cartilage 

 tube containing only blood vessels. In specimen B one of the branches 

 of this core contains one and the ether two continuations of the central 



* Loc. Cit., p. 33. 



f " Jlernoire sur les especes indigenes du genre Laccrta." Ann. d«a Sciences Naturelleo 

 F8'29, XVI, p. 337. 



§ ■"■ Die Regeneration von Geweben und Organen beiden Wifbelthieren? besoadets 

 Amphibien and Reptilien," Cassel, 1885, 



17 



