152 REPTILES 



immediately makes its tail as rigid as a steel-rod ; and while in 

 this condition a slight amount of force is sufficient to cause a 

 complete or partial fracture of this appendage. If the fracture 

 be complete, the tail, when the reptile has been seized, will 

 remain in the hand of the would-be captor, while the lizard 

 itself will run or wriggle off apparently none the worse for the 

 voluntary amputation. When the fracture is incomplete, a 

 transverse crack will be noticed on the under surface of the tail, 

 the upper side of which exhibits no sign of injury. Seeing 

 that a lizard or slow-worm flying from an enemy would more 

 probably be seized by the tail than by any other part, it is 

 obvious that the power of voluntarily separating that member 

 must be a great protective advantage. 



In all lizards endowed with this power of tail-amputation 

 the centra, or bodies, of the caudal vertebrae are traversed by a 

 cartilaginous transverse division, or septum ; and it is at one or 

 other of these lines of weakness that the tail snaps. For a 

 long time this was regarded as a satisfactory explanation of the 

 phenomenon ; but it has been pointed out that this is not the 

 cause of the fracture taking place, and in some instances, at 

 any rate, seems to have nothing at all to do with it Dr. G. B. 

 Leighton, for instance, in his Life-History of British Lizards, 

 states that he has observed cases where the fracture took place 

 at the junction of two adjacent vertebras and not in the middle 

 of one. As the result of observation, coupled with dissection, 

 Dr. Leighton is indeed led to conclude, " that fracture of the 

 tail in the green lizard, as in the slow-worm, depends mainly 

 upon the peculiar arrangement of muscles and integument ; 

 that this fracture takes place, or may do, at definite intervals 

 corresponding to the end of every second caudal scale ; and 

 that this position as regards the caudal vertebrae was at an in- 

 tervertebral articulation. Given a fracture at any point, one 

 may say with certainty where any other fracture may occur, by 

 simply counting the scales ; the other fractures will be only at 

 the ends of the rows of scales numbering 2, 4, 6, 8, 10, and so 

 on, from the first fractured point. It should be added that the 

 explanation here offered to account for the fragility of the tail 

 is not an accepted view, but it is one which any observant field- 

 naturalist can examine for himself on the first slow-worm he 

 encounters," 



