CAUDAL ABNORMALITY IN LIZARDS, 689 



probable that the more complex cases are the result of more frequent 

 chance interference with the process of regrowth of the tail than obtained 

 in those instances wherein the new structure is merely bifid. It may 

 here be noted that none of the cases are examples of true axial duplicity, 

 as in the bifid cases one of the branches and in the trifid cases two of 

 the branches have the structure of a reproduced tail, and therefore 

 contain no portion of the vertebral column. I do not know of any 

 record of true axial duplicity involving the vertebral column in a lizard. 



It seems clear that the nonnal tail possesses a latent tendency to 

 develope outgrowths having the same struoture as that which arises in 

 continuation of the main axis after an accidental or reflex rupture ; and 

 moreover that these special growths, whether axial or lateral, have a 

 latent tendency to branch. But for the present it is not possible to 

 offer any explanation of these inherent tendencies or of the causes 

 which from time to time call them into play. 



I must express my thanks to Dr. S. F. Harmer, Superintendent of 

 the Cambridge University Museum of Zoology, for many facilities in 

 connection with the examination of specimens therein, and to Mr. W. 

 Bateson, F.R.S., for information on certain points and in connection with 

 the literature of the subject. 



Explanation oe the Plate. 



Figs. 1 to 6. Mabuia carinata. — Purely diagrammatic representations 

 of the arrangement of the scales of the tail in transverse section. The 

 sections are represented as seen from behind, so that right and left of 

 the plate are right and left of the sections. 



Large scales of the median ventral series shown in black. 



„ „ „ „ dorsal „ „ shaded. 



Small „ , 5 lateral series shown in outline. 



1. Specimens A and B. Normal region of tail. 



2. „ „ „ 1, Reproduced region, undivided 



proximal portion. 



3. Specimen A. Left branch. 



4. „ „ Right „ 



5. „ B. Dorsal „ 



6. „ „ Ventral „ 



Fig. 7. Calotes cristatellus. Dorsal surface of extremity of tail, 



natural size X about If. 

 „ 8. Lacerta muralis. Dorsal surface of left hind leg with tail- 

 like outgrowth, natural size X about 2, 

 ., 9. Anolis grahami. Ventral surfac9 ? natural size X 1§. 



