170 THE VIVARIUM. 
is rather common; but this is another fallacy concerning this 
Reptile. The most active Snake is not able to jump a distance 
greater than about two-thirds of its own length. 
I have heard people say, and have also seen it gravely asserted 
in books, that a poisonous Snake can easily be distinguished from 
a non-poisonous one by the greater thickness of its tail, and the 
greater bluntness of its head. This is a dangerous delusion. 
There are no outward signs by which all Snakes may be known as 
either venomous or not. Indeed, some Snakes which have a most 
noxious aspect, are quite harmless, and the reverse. If one be in 
doubt in regard to the character of a Snake, it is wise to hold the 
Reptile quite close to its head, firmly and carefully with one 
hand, while the other hand opens its mouth by the help of a 
small ivory paper-knife or similar article, and a search is made in 
the upper jaws for the fangs. However, it is much wiser for the 
amateur to have nothing to do with a Snake concerning whose 
harmlessness there can be any doubt. 
There has been a great deal said and written from time to time 
about ovo-viviparous Snakes opening their mouth when danger is 
threatening their young and allowing them to take refuge within 
the maternal body. I will not venture to class this statement among 
the popular delusions concerning Snakes, yet I fear it to be but a 
delusion after all. It cannot very well be proved untrue, but, on 
the other hand, it has never been, I believe, satisfactorily proved 
to be true. 
The common English Viper (Vipera berus) is one of the Snakes 
which is said to receive its young within its mouth in times of 
danger. People, but not naturalists, have frequently told me 
that they have seen the Viper thus refuging her young. Living 
in a county in which Vipers are common, I meet with many of 
them during the spring and summer months of the year; but I 
have never, I am sorry to say, witnessed such an act of motherly 
devotion on the part of these handsome little Snakes. That this 
proves nothing, either one way or the other, goes without saying. 
Still, if the habit were really so common as it is reported to be, I 
should have had a good chance of seeing it. 
A mistake, under the circumstances, can easily be made. In 
support of which assertion I venture to quote the following, taken 
