STUDY OF REPTILES 



as many as two dozen may be found together in a common 

 burrow. 



Why is the slow-worm not a snake ? The most convincing 

 reasons are beyond the reach of school- work. Slow- worms differ 

 entirely from snakes as regards their skull, their scales, their ribs, 

 and their soft parts, and they always show traces of the pectoral 

 girdle and pelvic girdle, whereas snakes never -show any trace of 

 the former, and only in rare cases (boas and pythons) of the latter. 

 It is easy to show, however, that the slow-worm has a long tail, 

 while the snake has a short tail (without ribs), and that the 

 slow-worm has movable eyelids, while these are quite rudimentary 

 in snakes. * 



(4) The adder or viper Viper a berus is widely distributed in 

 the wilder parts of Britain, especially on heaths and moors, and 

 in mixed woods 



left between the 

 fields. It feeds 

 mainly on mice, 

 which it paralyses 

 with its poisonous 

 bite. 



An adder may 

 attain a length of 

 two feet or a little 

 more, but a foot 

 and a half is a 



common length. The colour is very variable, grey, brown, 

 reddish, black, but there is usually a dark zigzag line along the 

 middle line of the back and a dark St. Andrew's cross on the 

 back of the head. 



Adders are mainly nocturnal in their activities. During the 

 day they often bask on a warm dry spot. They pair in spring, 

 and bring forth young in midsummer. They hibernate all through 

 the winter, and dozens are sometimes found together. The adder 

 cannot be kept captive ; it starves itself to death. 



(5) The grass snake Tropidonotus natrix is widely distributed 

 in England and is the largest of the three British snakes, being 

 often about a yard in length. It is quite harmless, and though 



VOL. I. 8 



FIG. 33. The adder Vipera berus showing the 

 zigzag black mark along the middle line of 

 the back. This is often very indistinct. Its 

 head is distinctly separated from the neck ; it 

 bears, as the figure shows, small scales and a 

 few larger shields. The specimen shows two 

 diverging black streaks on the back of the 

 head ; others show a St. Andrew's cross in the 

 same position. 



