ADAPTATIONS TO SPECIAL ENDS 145 



glands of other animals. A dense fibrous sheath, overlain by a 

 stratum of powerful muscle, invests the poison-gland. When 

 these snakes open their mouths to strike, a special arrangement 

 (into the details of which it is unnecessary to enter) erects the 

 venom-fangs, while at the same time the muscles compress the 

 venom-glands in the same manner as an india-rubber surgical 

 syringe is squeezed by the grasp of the hand, and with such 

 force that when the snake misses its aim or is irritated without 

 having anything at which to bite, the fluid is spurted a consider- 

 able distance from the hollow summits of the fangs. The ar- 

 rangement is perfect, conveying the venom into the heart of 

 the wound ; if it had been devised by human skill for killing 

 enemies, it might have been described as a fiendish invention. 

 The nature, properties and effects of snake-poison need not be 

 discussed. 



Since the chapter on the food of reptiles was printed off it 

 has been recorded that a viper ( Vipera macrops) inhabiting 

 Bosnia and Herzegovina feeds almost exclusively on grass- 

 hoppers. Although retaining the venom-fangs characteristic 

 of its tribe, this viper, which grows to a length of about 18 

 inches, is stated to show no disposition to bite when handled, 

 and only attempts to do so when seriously injured. This 

 species is near akin to V. ursinii of lower Austria (which, 

 although feeding on lizards and mice, is also stated to show 

 little or no disposition to bite), and thus to the typical viper. 

 It may be added that the food of the small North American 

 colubrine snakes of the genus Contia consists of caterpillars, 

 crickets, grasshoppers, spiders, etc. 



Venom-glands and venom-fangs are, however, by no means 

 the exclusive attributes of snakes^ at least according to general 

 acceptation, for they occur in the American lizards of the genus 

 Heloderma, to which allusion has been already made in con- 

 nection with colour. These lizards inhabit Central America, 

 Mexico, and Arizona, and are supposed to be represented by 

 two species, one of which is popularly known as the gila 

 monster. Since, however, the two forms differ chiefly, if not 

 entirely, in the matter of colour, it is perhaps permissible to 

 regard them as local races of a single species. These lizards 

 are unique in possessing the power of injecting poison into the 

 wounds made by their teeth in the same manner as venomous 



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