ADAPTATIONS TO SPECIAL ENDS 



3.3 



This voluntary tail-amputation, as already mentioned, is a 

 defensive measure. Although the regeneration of such lost 

 tails has nothing to do with either defence or attack, it may 

 nevertheless be referred to in this place. Lizards or slow- 

 worms which have thus voluntarily parted with their tails, al- 

 ways grow new ones, although there does not appear to be 

 evidence how often this process of amputation and regeneration 

 may be repeated in the same individual. Not infrequently the 

 new tail is double, or even triple ; while occasionally a small 

 extra tail may grow from the spot where the proper tail has 

 been partially fractured. More curious still is the circumstance 

 that in certain cases (although not in the slow-worm and the 

 green lizard and its allies) the scaling of the new tail is of a dif- 

 ferent type to that of the original one, being simpler, and some- 

 times at any rate displaying what appears to be the ancestral 

 form. The regenerated tail is indeed but a makeshift affair, for 

 it lacks true vertebrae, being supported merely by an unjointed 

 rod of fibrous cartilage. Nor is this difficult to account for, 

 seeing that the spinal cord could not be renewed, and that it is 

 only around this cord that vertebrae are ever developed. 

 Whether the " bogus " tail is capable of being cast and replaced, 

 history telleth not. As to the length of time required to grow 

 a new tail, it is stated that a pair of geckos which lost their 

 tails at the time of capture grew new stumps nearly half an 

 inch in length after six weeks confinement in a box without 

 food. 



The remarkable "rattle" from which the American snakes 

 of the genus Crotalus derive their title is an organ whose func- 

 tion is somewhat difficult to determine. Whatever this may be, 

 the apparatus may be appropriately referred to in this place. 

 The rattle forms the termination of the tail in these snakes, 

 and consists of a number of hollow horny structures, somewhat 

 like miniature Swiss sheep-bells, fitting into one another. The 

 terminal bell, which is of course the oldest of the series, is really 

 the horny sheath of the tip of the tail, which was shed but 

 remained attached to the new covering. Similarly each time 

 the skin of the snake is changed, the horny tail-sheath becomes 

 detached, but is retained in position by the new skin, and thus 

 forms the latest addition to the rattle. In course of time as 

 many as a dozen, or, in exceptional cases, even a score, of mov- 



