104 BRITISH LIZARDS 



A^njyhihia and Reptiles goes into some detail on the 

 point. He says (p. 495): "The caudal vertebrse of 

 the Geckones and of most Lacertoe are liable to break 

 across, like those of Sphenodon. They are enabled to 

 do this owing to a transverse spHt, which makes its 

 appearance with the ossification of the vertebral bodies 

 and extends later into and across the neural arch and 

 the various lateral processes. This split is ultimately 

 referable to a transverse septum of cartilage, wrongly 

 called chordal cartilage, which develops in the shell of 

 the body of the vertebra, destroys the chorda, and 

 extends peripherally. The cells of this septum retain 

 throughout life their juvenile quasi-embryonic char- 

 acter. When the tail is broken off — and this always 

 happens at such a septum — the cells of the remaining 

 half reproduce a new tail." Again, Dr. Gadow, on 

 p. 503 of the same work, says : " Each vertebral 

 centrum consists of a cartilaginous tube, more or less 

 calcified or ossified, with a narrow waist and a car- 

 tilaginous septum in the middle. In the tail this 

 septum, which is only slightly invaded by ossification, 

 coincides exactly with the line of transverse division 

 of the vertebrae into an anterior and a posterior half. 

 This is the level where the tail breaks off and whence 

 it is renewed." 



We may therefore say that the accepted explanation 

 of the phenomenon of the fragility of the tail in some 

 lizards, is that it is due to a peculiar condition of the 

 vertebrae, namely, the development of a cartilaginous 



