ZOOLOGY 



SECT. 



and Worms. All the rest prey on vertebrates of various kinds, 

 Fishes, Frogs, Lizards, Snakes, Birds and their eggs, and Mammals. 

 The Pythons and Boas kill their prey by constriction, winding 

 their body closely round it and drawing the coils tight till the 

 victim is crushed or asphyxiated. Some other non-venomous 

 Snakes kill with bites of their numerous sharp teeth. The 

 venomous Snakes sometimes, when the prey is a small and weak 

 animal such as a Frog, swallow it alive : usually they kill it with 

 the venom of their poison-fangs. 



When a venomous Snake strikes, the poison is pressed out from 

 the poison-gland by the contraction of the masseter (Fig. 950, 

 Me), one of the muscles which raise the lower jaw ; it is thus 

 forced along the duct (Gc) to the aperture (za), and injected 

 into the wound made by the fang. The effect is to produce 

 acute pain with increasing lethargy and weakness, and in the 



*fr * Km 



FIG. SoO. Poison apparatus of Rattlesnake. A, eye ; Ge, poison-duct entering the poison- 

 fang at t ; Km, musics of mastication partly cut through at * ; Me. constrictor muscle ; Me'. 

 continuation of the constrictor muscle to the lower jaw ; N. nasal opening ; S, fibrous poison - 

 sac ; Z, tongue ; Za, opening of the poison-duct ; Zj\ pouch of mucous membrane enclosing 

 the poison-fangs. (From Wiedersheim.) 



case of the venom of some kinds of Snakes, paralysis. Accord- 

 ing to the amount of the poison injected (in relation to the 

 size of the animal) and the degree of its virulence (which 

 differs not only in different kinds of Snakes, but in the same 

 Snake under different conditions) the symptoms may result in 

 death, or the bitten animal may recover. The poison is a clear, 

 slightly straw-coloured or greenish liquid; it preserves its 

 venomous properties for an indefinite period, even if completely 

 desiccated. The poisonous principles are certain proteids not to 

 be distinguished chemically from other proteids which have no 

 such poisonous properties. Immunity against the effects of the 

 poison, and relief of the symptoms after a bite has been inflicted, 

 have been found to be conferred by injections of the serum of 

 animals which have been treated with injections of increasing- 

 doses of the poison. 



The majority of Snakes are viviparous. Some, however, lay 



