THE PRINCIPAL SPECIES OF POISONOUS SNAKES fai 
body becomes twice the ordinary size. It then doubles back its 
head and neck in the shape of an $S, and emits a loud and 
prolonged hiss. Before biting, it first strikes a blow with its head 
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Fic, 37.—Bitis arietans (the Puff Adder). (After Duméril and Bibron. 
as with a battering-ram, thus justifying its French name, vipére 
heurtante (Striking Viper). 
The natives of South Africa assert that this Viper is able to 
